[PATCH v5 0/1] get page size using sysconf (_SC_PAGESIZE) instead of PAGE_SIZE

[PATCH v5 0/1] get page size using sysconf (_SC_PAGESIZE) instead of PAGE_SIZE

[Zied Guermazi]

get page size using sysconf (_SC_PAGESIZE) instead of PAGE_SIZE

Zied Guermazi (1):
  get page size using sysconf (_SC_PAGESIZE) instead of PAGE_SIZE

 gdb/nat/linux-btrace.c | 43 ++++++++++++++++++++++++++++--------------
 1 file changed, 29 insertions(+), 14 deletions(-)

-- 
2.25.1

[PATCH v5 1/1] get page size using sysconf (_SC_PAGESIZE) instead of PAGE_SIZE

[Zied Guermazi]

Currently, linux-btrace.c is only built when the host is x86 or x86_64 GNU/Linux.
Later patches will add btrace support on ARM processors using ARM Coresight ETM traces.
That ran into the fact that PAGE_SIZE is not defined on Aarch64.  This patch fixes that
by getting the page size value at runtime using POSIX sysconf(_SC_PAGESIZE) instead.

---
 gdb/nat/linux-btrace.c | 43 ++++++++++++++++++++++++++++--------------
 1 file changed, 29 insertions(+), 14 deletions(-)

diff --git a/gdb/nat/linux-btrace.c b/gdb/nat/linux-btrace.c
index b0d6dcd7cf1..d99ec8e01e3 100644
--- a/gdb/nat/linux-btrace.c
+++ b/gdb/nat/linux-btrace.c
@@ -445,6 +445,17 @@ diagnose_perf_event_open_fail ()
   error (_("Failed to start recording: %s"), safe_strerror (errno));
 }
 
+/* Returns System page size.  */
+
+static long
+system_page_size ()
+{
+  long page_size = sysconf (_SC_PAGESIZE);
+  if (page_size == -1)
+    perror_with_name (_("Failed to get system page size"));
+  return page_size;
+}
+
 /* Enable branch tracing in BTS format.  */
 
 static struct btrace_target_info *
@@ -486,9 +497,10 @@ linux_enable_bts (ptid_t ptid, const struct btrace_config_bts *conf)
   if (fd.get () < 0)
     diagnose_perf_event_open_fail ();
 
+  long page_size = system_page_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;
@@ -507,17 +519,17 @@ 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 * (__u64) 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 + (size_t) page_size;
 
       /* Check for overflows.  */
-      if ((__u64) length != data_size + PAGE_SIZE)
+      if ((__u64) length != data_size + (__u64) page_size)
 	continue;
 
       errno = 0;
@@ -532,7 +544,7 @@ 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 = (__u64) page_size;
 
 #if defined (PERF_ATTR_SIZE_VER5)
   if (offsetof (struct perf_event_mmap_page, data_size) <= header->size)
@@ -630,8 +642,9 @@ 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,
-		    fd.get (), 0);
+  long page_size = system_page_size ();
+  scoped_mmap data (nullptr, (size_t) 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));
 
@@ -641,8 +654,8 @@ 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;
@@ -661,7 +674,7 @@ 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 * (__u64) page_size;
 
       /* Don't ask for more than we can represent in the configuration.  */
       if ((__u64) UINT_MAX < data_size)
@@ -732,7 +745,8 @@ 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 = system_page_size ();
+  munmap ((void *) tinfo->header, (size_t) (tinfo->bts.size + page_size));
   close (tinfo->file);
 
   return BTRACE_ERR_NONE;
@@ -743,8 +757,9 @@ 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 = system_page_size ();
+  munmap ((void *) tinfo->pt.mem, tinfo->pt.size);
+  munmap ((void *) tinfo->header, (size_t) page_size);
   close (tinfo->file);
 
   return BTRACE_ERR_NONE;
-- 
2.25.1

RE: [PATCH v5 1/1] get page size using sysconf (_SC_PAGESIZE) instead of PAGE_SIZE

[Metzger, Markus T]

Hello Zied,

>Currently, linux-btrace.c is only built when the host is x86 or x86_64 GNU/Linux.
>Later patches will add btrace support on ARM processors using ARM Coresight
>ETM traces.
>That ran into the fact that PAGE_SIZE is not defined on Aarch64.  This patch fixes
>that
>by getting the page size value at runtime using POSIX sysconf(_SC_PAGESIZE)
>instead.

The patch looks good to me with one nit.

>+/* Returns System page size.  */
>+
>+static long
>+system_page_size ()
>+{
>+  long page_size = sysconf (_SC_PAGESIZE);
>+  if (page_size == -1)
>+    perror_with_name (_("Failed to get system page size"));
>+  return page_size;
>+}

We should cast PAGE_SIZE to some unsigned type, e.g. size_t, here, instead of
at each use below.

Regards,
Markus.
Intel Deutschland GmbH
Registered Address: Am Campeon 10, 85579 Neubiberg, Germany
Tel: +49 89 99 8853-0, www.intel.de <http://www.intel.de>
Managing Directors: Christin Eisenschmid, Sharon Heck, Tiffany Doon Silva  
Chairperson of the Supervisory Board: Nicole Lau
Registered Office: Munich
Commercial Register: Amtsgericht Muenchen HRB 186928