Re: [PATCH v6 4/7] start/stop btrace with coresight etm and collect etm buffer on linux os

[Luis Machado <luis.machado@linaro.org>]

On 5/31/21 6:33 PM, Zied Guermazi wrote:
> This patch implement the lower layer for starting ad stopping
> ARM CoreSight tracing on linux targets for arm and aarch64
> 
> gdb/ChangeLog
> 
> 	* nat/linux-btrace.h (btrace_tinfo_etm): New.
> 	(btrace_target_info): add etm.
> 	* nat/linux-btrace.c (linux_enable_bts): get page size from sysconf.
> 	(linux_enable_pt): get page size from sysconf.
> 	(perf_event_etm_event_type): New.
> 	(perf_event_etm_event_sink): New.
> 	(linux_enable_etm): New.
> 	(linux_enable_btrace): add enabling etm traces.
> 	(linux_disable_bts): get page size from sysconf.
> 	(linux_disable_pt): get page size from sysconf.
> 	(linux_disable_etm): New.
> 	(linux_disable_btrace): add disabling etm traces.
> 	(get_cpu_count): New.
> 	(cs_etm_is_etmv4): New.
> 	(cs_etm_get_register): New.
> 	(coresight_get_trace_id): New.
> 	(fill_etm_trace_params): New.
> 	(linux_fill_btrace_etm_config): New.
> 	(linux_read_etm): New.
> 	(linux_read_btrace): add reading etm traces.
> 	* arm-linux-nat.c (arm_linux_nat_target::enable_btrace): New.
> 	(arm_linux_nat_target::disable_btrace): New.
> 	(arm_linux_nat_target::teardown_btrace): New.
> 	(arm_linux_nat_target::read_btrace): New.
> 	(arm_linux_nat_target::btrace_conf): New.
> 	* aarch64-linux-nat.c (aarch64_linux_nat_target::enable_btrace): New.
> 	(aarch64_linux_nat_target::disable_btrace): New.
> 	(aarch64_linux_nat_target::teardown_btrace): New.
> 	(aarch64_linux_nat_target::read_btrace): New.
> 	(aarch64_linux_nat_target::btrace_conf): New.
> ---
>   gdb/aarch64-linux-nat.c |  68 +++++++
>   gdb/arm-linux-nat.c     |  68 +++++++
>   gdb/nat/linux-btrace.c  | 395 ++++++++++++++++++++++++++++++++++++++--
>   gdb/nat/linux-btrace.h  |  19 ++
>   4 files changed, 537 insertions(+), 13 deletions(-)
> 
> diff --git a/gdb/aarch64-linux-nat.c b/gdb/aarch64-linux-nat.c
> index 61224022f6a..4b629e1b3d2 100644
> --- a/gdb/aarch64-linux-nat.c
> +++ b/gdb/aarch64-linux-nat.c
> @@ -35,6 +35,7 @@
>   #include "nat/aarch64-linux.h"
>   #include "nat/aarch64-linux-hw-point.h"
>   #include "nat/aarch64-sve-linux-ptrace.h"
> +#include "nat/linux-btrace.h"
>   
>   #include "elf/external.h"
>   #include "elf/common.h"
> @@ -88,6 +89,17 @@ class aarch64_linux_nat_target final : public linux_nat_target
>     /* Override the GNU/Linux post attach hook.  */
>     void post_attach (int pid) override;
>   
> +  /* Override branch tracing.  */
> +  struct btrace_target_info *enable_btrace (ptid_t ptid,
> +				const struct btrace_config *conf) override;
> +  void disable_btrace (struct btrace_target_info *tinfo) override;
> +  void teardown_btrace (struct btrace_target_info *tinfo) override;
> +  enum btrace_error read_btrace (struct btrace_data *data,
> +				  struct btrace_target_info *btinfo,
> +				  enum btrace_read_type type) override;
> +  const struct btrace_config *btrace_conf (const struct btrace_target_info *)
> +				override;
> +
>     /* These three defer to common nat/ code.  */
>     void low_new_thread (struct lwp_info *lp) override
>     { aarch64_linux_new_thread (lp); }
> @@ -714,6 +726,62 @@ aarch64_linux_nat_target::post_attach (int pid)
>     linux_nat_target::post_attach (pid);
>   }
>   
> +/* Enable branch tracing.  */
> +
> +struct btrace_target_info *
> +aarch64_linux_nat_target::enable_btrace (ptid_t ptid,
> +					  const struct btrace_config *conf)
> +{
> +  struct btrace_target_info *tinfo = nullptr;
> +  try
> +    {
> +      tinfo = linux_enable_btrace (ptid, conf);
> +    }
> +  catch (const gdb_exception_error &exception)
> +    {
> +      error (_("Could not enable branch tracing for %s: %s"),
> +	     target_pid_to_str (ptid).c_str (), exception.what ());
> +    }
> +
> +  return tinfo;
> +}
> +
> +/* Disable branch tracing.  */
> +
> +void
> +aarch64_linux_nat_target::disable_btrace (struct btrace_target_info *tinfo)
> +{
> +  enum btrace_error errcode = linux_disable_btrace (tinfo);
> +
> +  if (errcode != BTRACE_ERR_NONE)
> +    error (_("Could not disable branch tracing."));

We should probably print the error code.

> +}
> +
> +/* Teardown branch tracing.  */
> +
> +void
> +aarch64_linux_nat_target::teardown_btrace (struct btrace_target_info *tinfo)
> +{
> +  /* Ignore errors.  */
> +  linux_disable_btrace (tinfo);
> +}
> +
> +enum btrace_error
> +aarch64_linux_nat_target::read_btrace (struct btrace_data *data,
> +				       struct btrace_target_info *btinfo,
> +				       enum btrace_read_type type)
> +{
> +  return linux_read_btrace (data, btinfo, type);
> +}
> +
> +/* See to_btrace_conf in target.h.  */
> +
> +const struct btrace_config *
> +aarch64_linux_nat_target::btrace_conf (const struct btrace_target_info *btinfo)
> +{
> +  return linux_btrace_conf (btinfo);
> +}
> +
>   /* Implement the "read_description" target_ops method.  */
>   
>   const struct target_desc *
> diff --git a/gdb/arm-linux-nat.c b/gdb/arm-linux-nat.c
> index 880ac0da044..32631b33328 100644
> --- a/gdb/arm-linux-nat.c
> +++ b/gdb/arm-linux-nat.c
> @@ -39,6 +39,7 @@
>   #include <sys/procfs.h>
>   
>   #include "nat/linux-ptrace.h"
> +#include "nat/linux-btrace.h"
>   #include "linux-tdep.h"
>   
>   /* Prototypes for supply_gregset etc.  */
> @@ -95,6 +96,17 @@ class arm_linux_nat_target final : public linux_nat_target
>   
>     const struct target_desc *read_description () override;
>   
> +  /* Override branch tracing.  */
> +  struct btrace_target_info *enable_btrace (ptid_t ptid,
> +				const struct btrace_config *conf) override;
> +  void disable_btrace (struct btrace_target_info *tinfo) override;
> +  void teardown_btrace (struct btrace_target_info *tinfo) override;
> +  enum btrace_error read_btrace (struct btrace_data *data,
> +				  struct btrace_target_info *btinfo,
> +				  enum btrace_read_type type) override;
> +  const struct btrace_config *btrace_conf (const struct btrace_target_info *)
> +				override;
> +
>     /* Override linux_nat_target low methods.  */
>   
>     /* Handle thread creation and exit.  */
> @@ -1190,6 +1202,62 @@ arm_linux_nat_target::watchpoint_addr_within_range (CORE_ADDR addr,
>     return start <= addr && start + length - 1 >= addr;
>   }
>   
> +/* Enable branch tracing.  */
> +
> +struct btrace_target_info *
> +arm_linux_nat_target::enable_btrace (ptid_t ptid,
> +				     const struct btrace_config *conf)
> +{
> +  struct btrace_target_info *tinfo = nullptr;
> +  try
> +    {
> +      tinfo = linux_enable_btrace (ptid, conf);
> +    }
> +  catch (const gdb_exception_error &exception)
> +    {
> +      error (_("Could not enable branch tracing for %s: %s"),
> +	     target_pid_to_str (ptid).c_str (), exception.what ());
> +    }
> +
> +  return tinfo;
> +}
> +
> +/* Disable branch tracing.  */
> +
> +void
> +arm_linux_nat_target::disable_btrace (struct btrace_target_info *tinfo)
> +{
> +  enum btrace_error errcode = linux_disable_btrace (tinfo);
> +
> +  if (errcode != BTRACE_ERR_NONE)
> +    error (_("Could not disable branch tracing."));

Same here. We should show the error code.

> +}
> +
> +/* Teardown branch tracing.  */
> +
> +void
> +arm_linux_nat_target::teardown_btrace (struct btrace_target_info *tinfo)
> +{
> +  /* Ignore errors.  */
> +  linux_disable_btrace (tinfo);
> +}
> +
> +enum btrace_error
> +arm_linux_nat_target::read_btrace (struct btrace_data *data,
> +				   struct btrace_target_info *btinfo,
> +				   enum btrace_read_type type)
> +{
> +  return linux_read_btrace (data, btinfo, type);
> +}
> +
> +/* See to_btrace_conf in target.h.  */
> +
> +const struct btrace_config *
> +arm_linux_nat_target::btrace_conf (const struct btrace_target_info *btinfo)
> +{
> +  return linux_btrace_conf (btinfo);
> +}
> +
>   /* Handle thread creation.  We need to copy the breakpoints and watchpoints
>      in the parent thread to the child thread.  */
>   void
> diff --git a/gdb/nat/linux-btrace.c b/gdb/nat/linux-btrace.c
> index 324f7ef0407..9ef182d774a 100644
> --- a/gdb/nat/linux-btrace.c
> +++ b/gdb/nat/linux-btrace.c
> @@ -32,6 +32,10 @@
>   
>   #include <sys/syscall.h>
>   
> +#if defined (HAVE_LIBOPENCSD_C_API)
> +#  include <opencsd/ocsd_if_types.h>
> +#endif
> +
>   #if HAVE_LINUX_PERF_EVENT_H && defined(SYS_perf_event_open)
>   #include <unistd.h>
>   #include <sys/mman.h>
> @@ -483,10 +487,11 @@ linux_enable_bts (ptid_t ptid, const struct btrace_config_bts *conf)
>     scoped_fd fd (syscall (SYS_perf_event_open, &bts->attr, pid, -1, -1, 0));
>     if (fd.get () < 0)
>       diagnose_perf_event_open_fail ();
> +  long page_size = sysconf (_SC_PAGESIZE);
>   
>     /* Convert the requested size in bytes to pages (rounding up).  */
> -  pages = ((size_t) conf->size / PAGE_SIZE
> -	   + ((conf->size % PAGE_SIZE) == 0 ? 0 : 1));
> +  pages = ((size_t) conf->size / page_size
> +	   + ((conf->size % page_size) == 0 ? 0 : 1));
>     /* We need at least one page.  */
>     if (pages == 0)
>       pages = 1;
> @@ -505,17 +510,17 @@ linux_enable_bts (ptid_t ptid, const struct btrace_config_bts *conf)
>         size_t length;
>         __u64 data_size;
>   
> -      data_size = (__u64) pages * PAGE_SIZE;
> +      data_size = (__u64) pages * page_size;
>   
>         /* Don't ask for more than we can represent in the configuration.  */
>         if ((__u64) UINT_MAX < data_size)
>   	continue;
>   
>         size = (size_t) data_size;
> -      length = size + PAGE_SIZE;
> +      length = size + page_size;
>   
>         /* Check for overflows.  */
> -      if ((__u64) length != data_size + PAGE_SIZE)
> +      if ((__u64) length != data_size + page_size)
>   	continue;
>   
>         errno = 0;
> @@ -530,7 +535,7 @@ linux_enable_bts (ptid_t ptid, const struct btrace_config_bts *conf)
>   
>     struct perf_event_mmap_page *header = (struct perf_event_mmap_page *)
>       data.get ();
> -  data_offset = PAGE_SIZE;
> +  data_offset = page_size;
>   
>   #if defined (PERF_ATTR_SIZE_VER5)
>     if (offsetof (struct perf_event_mmap_page, data_size) <= header->size)
> @@ -613,7 +618,8 @@ linux_enable_pt (ptid_t ptid, const struct btrace_config_pt *conf)
>       diagnose_perf_event_open_fail ();
>   
>     /* Allocate the configuration page. */
> -  scoped_mmap data (nullptr, PAGE_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED,
> +  long page_size = sysconf (_SC_PAGESIZE);
> +  scoped_mmap data (nullptr, page_size, PROT_READ | PROT_WRITE, MAP_SHARED,
>   		    fd.get (), 0);
>     if (data.get () == MAP_FAILED)
>       error (_("Failed to map trace user page: %s."), safe_strerror (errno));
> @@ -624,8 +630,8 @@ linux_enable_pt (ptid_t ptid, const struct btrace_config_pt *conf)
>     header->aux_offset = header->data_offset + header->data_size;
>   
>     /* Convert the requested size in bytes to pages (rounding up).  */
> -  pages = ((size_t) conf->size / PAGE_SIZE
> -	   + ((conf->size % PAGE_SIZE) == 0 ? 0 : 1));
> +  pages = ((size_t) conf->size / page_size
> +	   + ((conf->size % page_size) == 0 ? 0 : 1));
>     /* We need at least one page.  */
>     if (pages == 0)
>       pages = 1;
> @@ -644,7 +650,7 @@ linux_enable_pt (ptid_t ptid, const struct btrace_config_pt *conf)
>         size_t length;
>         __u64 data_size;
>   
> -      data_size = (__u64) pages * PAGE_SIZE;
> +      data_size = (__u64) pages * page_size;
>   
>         /* Don't ask for more than we can represent in the configuration.  */
>         if ((__u64) UINT_MAX < data_size)
> @@ -689,6 +695,154 @@ linux_enable_pt (ptid_t ptid, const struct btrace_config_pt *conf)
>   
>   #endif /* !defined (PERF_ATTR_SIZE_VER5) */
>   
> +/* Determine the etm event type.  */
> +
> +static int
> +perf_event_etm_event_type ()
> +{
> +  static const char filename[] = "/sys/bus/event_source/devices/cs_etm/type";
> +
> +  errno = 0;
> +  gdb_file_up file = gdb_fopen_cloexec (filename, "r");
> +  if (file.get () == nullptr)
> +    error (_("Failed to open %s: %s."), filename, safe_strerror (errno));
> +
> +  int type, found = fscanf (file.get (), "%d", &type);
> +  if (found != 1)
> +    error (_("Failed to read the ETM event type from %s."), filename);
> +
> +  return type;
> +}
> +
> +/* Get the sink hash to use in the event attributes.  */
> +
> +static unsigned int
> +perf_event_etm_event_sink (const struct btrace_config_etm *conf)
> +{
> +  char filename[PATH_MAX];
> +
> +  snprintf (filename, PATH_MAX,
> +	    "/sys/bus/event_source/devices/cs_etm/sinks/%s", conf->sink);
> +  errno = 0;
> +  gdb_file_up file = gdb_fopen_cloexec (filename, "r");
> +  if (file.get () == nullptr)
> +    error (_("Failed to open %s: %s."), filename, safe_strerror (errno));
> +
> +  unsigned int sink;
> +  int  found = fscanf (file.get (), "0x%x", &sink);
> +  if (found != 1)
> +    error (_("Failed to read the ETM sink from %s."), filename);
> +
> +  return sink;
> +}
> +
> +/* Enable ARM CoreSight ETM tracing.  */
> +
> +static struct btrace_target_info *
> +linux_enable_etm (ptid_t ptid, const struct btrace_config_etm *conf)
> +{
> +  struct btrace_tinfo_etm *etm;
> +  size_t pages;
> +  int pid, pg;
> +
> +  pid = ptid.lwp ();
> +  if (pid == 0)
> +    pid = ptid.pid ();
> +
> +  gdb::unique_xmalloc_ptr<btrace_target_info> tinfo
> +    (XCNEW (btrace_target_info));
> +  tinfo->ptid = ptid;
> +
> +  tinfo->conf.format = BTRACE_FORMAT_ETM;
> +  etm = &tinfo->variant.etm;
> +
> +  etm->attr.type = perf_event_etm_event_type ();
> +  etm->attr.size = sizeof (etm->attr);
> +
> +  etm->attr.sample_type = PERF_SAMPLE_CPU;
> +  etm->attr.read_format = PERF_FORMAT_ID;
> +  etm->attr.sample_id_all = 1;
> +  etm->attr.enable_on_exec = 1;
> +  etm->attr.exclude_kernel = 1;
> +  etm->attr.exclude_hv = 1;
> +  etm->attr.exclude_idle = 1;
> +  if (conf->sink != nullptr)
> +    {
> +      if (strcmp (conf->sink, "default") != 0)
> +	etm->attr.config2 = perf_event_etm_event_sink (conf);
> +    }
> +
> +  errno = 0;
> +  scoped_fd fd (syscall (SYS_perf_event_open, &etm->attr, pid, -1, -1, 0));
> +  if (fd.get () < 0)
> +    diagnose_perf_event_open_fail ();
> +
> +  /* Allocate the configuration page.  */
> +  long page_size = sysconf (_SC_PAGESIZE);
> +  scoped_mmap data (nullptr, page_size, PROT_READ | PROT_WRITE, MAP_SHARED,
> +		    fd.get (), 0);
> +  if (data.get () == MAP_FAILED)
> +    error (_("Failed to map trace user page: %s."), safe_strerror (errno));
> +
> +  struct perf_event_mmap_page *header = (struct perf_event_mmap_page *)
> +    data.get ();
> +
> +  header->aux_offset = header->data_offset + header->data_size;
> +  /* Convert the requested size in bytes to pages (rounding up).  */
> +  pages = ((size_t) conf->size / page_size
> +	   + ((conf->size % page_size) == 0 ? 0 : 1));
> +  /* We need at least one page.  */
> +  if (pages == 0)
> +    pages = 1;
> +
> +  /* The buffer size can be requested in powers of two pages.  Adjust PAGES
> +     to the next power of two.  */
> +  for (pg = 0; pages != ((size_t) 1 << pg); ++pg)
> +    if ((pages & ((size_t) 1 << pg)) != 0)
> +      pages += ((size_t) 1 << pg);
> +
> +  /* We try to allocate the requested size.
> +     If that fails, try to get as much as we can.  */
> +  scoped_mmap aux;
> +  for (; pages > 0; pages >>= 1)
> +    {
> +      size_t length;
> +      __u64 data_size;
> +      data_size = (__u64) pages * page_size;
> +
> +      /* Don't ask for more than we can represent in the configuration.  */
> +      if ((__u64) UINT_MAX < data_size)
> +	continue;
> +
> +      length = (size_t) data_size;
> +
> +      /* Check for overflows.  */
> +      if ((__u64) length != data_size)
> +	continue;
> +
> +      header->aux_size = data_size;
> +
> +      errno = 0;
> +      aux.reset (nullptr, length, PROT_READ, MAP_SHARED, fd.get (),
> +		 header->aux_offset);
> +      if (aux.get () != MAP_FAILED)
> +	break;
> +    }
> +  if (pages == 0)
> +    error (_("Failed to map trace buffer: %s."), safe_strerror (errno));
> +
> +  etm->etm.size = aux.size ();
> +  etm->etm.mem = (const uint8_t *) aux.release ();
> +  etm->etm.data_head = &header->aux_head;
> +  etm->etm.last_head = header->aux_tail;
> +  etm->header = (struct perf_event_mmap_page *) data.release ();
> +  gdb_assert (etm->header == header);
> +  etm->file = fd.release ();
> +
> +  tinfo->conf.etm.size = (unsigned int) etm->etm.size;
> +  return tinfo.release ();
> +}
> +
>   /* See linux-btrace.h.  */
>   
>   struct btrace_target_info *
> @@ -707,6 +861,10 @@ linux_enable_btrace (ptid_t ptid, const struct btrace_config *conf)
>   
>       case BTRACE_FORMAT_PT:
>         return linux_enable_pt (ptid, &conf->pt);
> +
> +    case BTRACE_FORMAT_ETM:
> +      return linux_enable_etm (ptid, &conf->etm);
> +
>       }
>   }
>   
> @@ -715,7 +873,8 @@ linux_enable_btrace (ptid_t ptid, const struct btrace_config *conf)
>   static enum btrace_error
>   linux_disable_bts (struct btrace_tinfo_bts *tinfo)
>   {
> -  munmap((void *) tinfo->header, tinfo->bts.size + PAGE_SIZE);
> +  long page_size = sysconf (_SC_PAGESIZE);
> +  munmap ((void *) tinfo->header, tinfo->bts.size + page_size);
>     close (tinfo->file);
>   
>     return BTRACE_ERR_NONE;
> @@ -726,8 +885,22 @@ linux_disable_bts (struct btrace_tinfo_bts *tinfo)
>   static enum btrace_error
>   linux_disable_pt (struct btrace_tinfo_pt *tinfo)
>   {
> -  munmap((void *) tinfo->pt.mem, tinfo->pt.size);
> -  munmap((void *) tinfo->header, PAGE_SIZE);
> +  long page_size = sysconf (_SC_PAGESIZE);
> +  munmap ((void *) tinfo->pt.mem, tinfo->pt.size);
> +  munmap ((void *) tinfo->header, page_size);
> +  close (tinfo->file);
> +
> +  return BTRACE_ERR_NONE;
> +}
> +
> +/* Disable ARM CoreSight ETM tracing.  */
> +
> +static enum btrace_error
> +linux_disable_etm (struct btrace_tinfo_etm *tinfo)
> +{
> +  long page_size = sysconf (_SC_PAGESIZE);
> +  munmap ((void *) tinfo->etm.mem, tinfo->etm.size);
> +  munmap ((void *) tinfo->header, page_size);
>     close (tinfo->file);
>   
>     return BTRACE_ERR_NONE;
> @@ -753,6 +926,10 @@ linux_disable_btrace (struct btrace_target_info *tinfo)
>       case BTRACE_FORMAT_PT:
>         errcode = linux_disable_pt (&tinfo->variant.pt);
>         break;
> +
> +    case BTRACE_FORMAT_ETM:
> +      errcode = linux_disable_etm (&tinfo->variant.etm);
> +      break;
>       }
>   
>     if (errcode == BTRACE_ERR_NONE)
> @@ -898,6 +1075,190 @@ linux_read_pt (struct btrace_data_pt *btrace,
>     internal_error (__FILE__, __LINE__, _("Unknown btrace read type."));
>   }
>   
> +/* Return the number of CPUs that are present.  */
> +
> +static int
> +get_cpu_count (void)
> +{
> +  static const char filename[] = "/sys/devices/system/cpu/present";
> +
> +  gdb_file_up file = gdb_fopen_cloexec (filename, "r");
> +  if (file.get () == nullptr)
> +    error (_("Failed to open %s: %s."), filename, safe_strerror (errno));
> +
> +  fseek (file.get (), 0, SEEK_END);
> +  int length = ftell (file.get ());
> +  fseek (file.get (), 0, SEEK_SET);
> +
> +  char *buffer = (char *) xmalloc (length+1);
> +
> +  length = fread (buffer, 1, length, file.get ());
> +  buffer[length]='\0';
> +  while ((--length) != 0)
> +    {
> +      if ((buffer[length] == ',') || (buffer[length] == '-'))
> +	{
> +	  length++;
> +	  break;
> +	}
> +    }
> +
> +  int cpu_count;
> +  int found = sscanf (&buffer[length], "%d", &cpu_count);
> +  if (found < 1)
> +    error (_("Failed to get cpu count in %s: %s."),
> +	     buffer, safe_strerror (errno));
> +
> +  cpu_count ++;
> +  return (cpu_count);
> +}
> +
> +/* Check if the ETM is an etmv4.  */
> +
> +static bool
> +cs_etm_is_etmv4 (int cpu)
> +{
> +  char filename[PATH_MAX];
> +  snprintf (filename, PATH_MAX,
> +	    "/sys/bus/event_source/devices/cs_etm/cpu%d/trcidr/trcidr0", cpu);
> +  errno = 0;
> +  gdb_file_up file = gdb_fopen_cloexec (filename, "r");
> +  if (file.get () == nullptr)
> +    return false;
> +
> +  return true;
> +}
> +
> +/* Get etm configuration register from sys filesystem.  */
> +
> +static uint32_t
> +cs_etm_get_register (int cpu, const char *path)
> +{
> +  char filename[PATH_MAX];
> +
> +  /* Get coresight register from sysfs.  */
> +  snprintf (filename, PATH_MAX,
> +	    "/sys/bus/event_source/devices/cs_etm/cpu%d/%s", cpu, path);
> +  errno = 0;
> +  gdb_file_up file = gdb_fopen_cloexec (filename, "r");
> +  if (file.get () == nullptr)
> +    error (_("Failed to open %s: %s."), filename, safe_strerror (errno));
> +
> +  uint32_t val = 0;
> +
> +  int  found = fscanf (file.get (), "0x%x", &val);
> +  if (found != 1)
> +    error (_("Failed to read coresight register from %s."), filename);
> +  return val;
> +}
> +
> +#define CORESIGHT_ETM_PMU_SEED  0x10
> +
> +/* Calculate trace_id for this cpu
> +   to be kept aligned with coresight-pmu.h.  */
> +
> +static inline int
> +coresight_get_trace_id (int cpu)
> +{
> +  return (CORESIGHT_ETM_PMU_SEED + (cpu * 2));
> +}
> +
> +/* PTMs ETMIDR[11:8] set to b0011.  */
> +#define ETMIDR_PTM_VERSION 0x00000300
> +
> +/* Collect and fill etm trace parameter.  */
> +
> +static void
> +fill_etm_trace_params (struct cs_etm_trace_params *etm_trace_params, int cpu)
> +{
> +  if (cs_etm_is_etmv4 (cpu) == true)
> +    {
> +      etm_trace_params->arch_ver = ARCH_V8;
> +      etm_trace_params->core_profile = profile_CortexA;
> +      etm_trace_params->protocol = OCSD_PROTOCOL_ETMV4I;
> +      /* This is the parameter passed in etm->attr.config in the call to
> +	 perf_event_open remapped according to linux/coresight-pmu.h.  */
> +      etm_trace_params->etmv4.reg_configr = 0;
> +      etm_trace_params->etmv4.reg_idr0
> +	 = cs_etm_get_register (cpu, "trcidr/trcidr0");
> +      etm_trace_params->etmv4.reg_idr1
> +	 = cs_etm_get_register (cpu, "trcidr/trcidr1");
> +      etm_trace_params->etmv4.reg_idr2
> +	 = cs_etm_get_register (cpu, "trcidr/trcidr2");
> +      etm_trace_params->etmv4.reg_idr8
> +	 = cs_etm_get_register (cpu, "trcidr/trcidr8");
> +      etm_trace_params->etmv4.reg_traceidr = coresight_get_trace_id (cpu);
> +    }
> +  else
> +    {
> +      etm_trace_params->arch_ver = ARCH_V7;
> +      etm_trace_params->core_profile = profile_CortexA;
> +      etm_trace_params->protocol
> +	= (etm_trace_params->etmv3.reg_idr & ETMIDR_PTM_VERSION)
> +	  == ETMIDR_PTM_VERSION ? OCSD_PROTOCOL_PTM : OCSD_PROTOCOL_ETMV3;
> +      etm_trace_params->etmv3.reg_ccer
> +	 = cs_etm_get_register (cpu, "mgmt/etmccer");
> +      etm_trace_params->etmv3.reg_ctrl
> +	 = cs_etm_get_register (cpu, "mgmt/etmcr");
> +      etm_trace_params->etmv3.reg_idr
> +	 = cs_etm_get_register (cpu, "mgmt/etmidr");
> +      etm_trace_params->etmv3.reg_trc_id
> +	 = cs_etm_get_register (cpu, "traceid");
> +    }
> +}
> +
> +static void
> +linux_fill_btrace_etm_config (struct btrace_target_info *tinfo,
> +			       struct btrace_data_etm_config *conf)
> +{
> +
> +  cs_etm_trace_params etm_trace_params;
> +  conf->cpu_count = get_cpu_count ();
> +  conf->etm_trace_params = new std::vector<cs_etm_trace_params>;
> +  for (int i = 0; i < conf->cpu_count; i++)
> +    {
> +      fill_etm_trace_params (&etm_trace_params,i);
> +      conf->etm_trace_params->push_back (etm_trace_params);
> +    }
> +
> +  conf->etm_decoder_params.formatted = 1;
> +  conf->etm_decoder_params.fsyncs = 0;
> +  conf->etm_decoder_params.hsyncs = 0;
> +  conf->etm_decoder_params.frame_aligned = 0;
> +  conf->etm_decoder_params.reset_on_4x_sync = 1;
> +}
> +
> +static enum btrace_error
> +linux_read_etm (struct btrace_data_etm *btrace,
> +		struct btrace_target_info *tinfo,
> +		enum btrace_read_type type)
> +{
> +  struct perf_event_buffer *etm;
> +  etm = &tinfo->variant.etm.etm;
> +
> +  linux_fill_btrace_etm_config (tinfo, &btrace->config);
> +
> +  switch (type)
> +    {
> +    case BTRACE_READ_DELTA:
> +      /* We don't support delta reads.  The data head (i.e. aux_head) wraps
> +	 around to stay inside the aux buffer.  */
> +      return BTRACE_ERR_NOT_SUPPORTED;
> +
> +    case BTRACE_READ_NEW:
> +      if (!perf_event_new_data (etm))
> +	return BTRACE_ERR_NONE;
> +
> +      /* Fall through.  */
> +    case BTRACE_READ_ALL:
> +      perf_event_read_all (etm, &(btrace->data),&(btrace->size));
> +      return BTRACE_ERR_NONE;
> +    }
> +
> +  internal_error (__FILE__, __LINE__, _("Unkown btrace read type."));
> +}
> +
> +
>   /* See linux-btrace.h.  */
>   
>   enum btrace_error
> @@ -924,6 +1285,14 @@ linux_read_btrace (struct btrace_data *btrace,
>         btrace->variant.pt.size = 0;
>   
>         return linux_read_pt (&btrace->variant.pt, tinfo, type);
> +
> +    case BTRACE_FORMAT_ETM:
> +      /* We read btrace in ARM CoreSight ETM Trace format.  */
> +      btrace->format = BTRACE_FORMAT_ETM;
> +      btrace->variant.etm.data = NULL;
> +      btrace->variant.etm.size = 0;
> +
> +      return linux_read_etm (&btrace->variant.etm, tinfo, type);
>       }
>   
>     internal_error (__FILE__, __LINE__, _("Unkown branch trace format."));
> diff --git a/gdb/nat/linux-btrace.h b/gdb/nat/linux-btrace.h
> index 607182da144..3038d2f45a0 100644
> --- a/gdb/nat/linux-btrace.h
> +++ b/gdb/nat/linux-btrace.h
> @@ -78,6 +78,22 @@ struct btrace_tinfo_pt
>     /* The trace perf event buffer.  */
>     struct perf_event_buffer pt;
>   };
> +
> +/* Branch trace target information for ARM CoreSight ETM Trace.  */
> +struct btrace_tinfo_etm
> +{
> +  /* The Linux perf_event configuration for collecting the branch trace.  */
> +  struct perf_event_attr attr;
> +
> +  /* The perf event file.  */
> +  int file;
> +
> +  /* The perf event configuration page.  */
> +  volatile struct perf_event_mmap_page *header;
> +
> +  /* The trace perf event buffer.  */
> +  struct perf_event_buffer etm;
> +};
>   #endif /* HAVE_LINUX_PERF_EVENT_H */
>   
>   /* Branch trace target information per thread.  */
> @@ -98,6 +114,9 @@ struct btrace_target_info
>   
>       /* CONF.FORMAT == BTRACE_FORMAT_PT.  */
>       struct btrace_tinfo_pt pt;
> +
> +    /* CONF.FORMAT == BTRACE_FORMAT_ETM.  */
> +    struct btrace_tinfo_etm etm;
>     } variant;
>   #endif /* HAVE_LINUX_PERF_EVENT_H */
>   };
> 

Otherwise looks OK to me.