[PATCH v2 2/4] libdw: Try .dwp file in __libdw_find_split_unit()

[Omar Sandoval <osandov@osandov.com>]

From: Omar Sandoval <osandov@fb.com>

Try opening the file in the location suggested by the standard (the
skeleton file name + ".dwp") and looking up the unit in the package
index.  The rest is similar to .dwo files, with slightly different
cleanup since a single Dwarf handle is shared.

	* libdw/libdw_find_split_unit.c (try_dwp_file): New function.
	(__libdw_find_split_unit): Call try_dwp_file.
	* libdw/libdwP.h (Dwarf): Add dwp_dwarf and dwp_fd.
	(__libdw_dwp_findcu_id): New declaration.
	(__libdw_link_skel_split): Handle .debug_addr for dwp.
	* libdw/libdw_begin_elf.c (dwarf_begin_elf): Initialize
	result->dwp_fd.
	* libdw/dwarf_end.c (dwarf_end): Free dwarf->dwp_dwarf and close
	dwarf->dwp_fd.
	(cu_free): Don't free split dbg if it is dwp_dwarf.

Signed-off-by: Omar Sandoval <osandov@fb.com>
---
 libdw/dwarf_begin_elf.c           |  1 +
 libdw/dwarf_cu_dwp_section_info.c | 19 ++++++++
 libdw/dwarf_end.c                 | 10 ++++-
 libdw/libdwP.h                    | 23 ++++++++--
 libdw/libdw_find_split_unit.c     | 75 ++++++++++++++++++++++++++++---
 5 files changed, 119 insertions(+), 9 deletions(-)

diff --git a/libdw/dwarf_begin_elf.c b/libdw/dwarf_begin_elf.c
index 323a91d0..ca2b7e2a 100644
--- a/libdw/dwarf_begin_elf.c
+++ b/libdw/dwarf_begin_elf.c
@@ -567,6 +567,7 @@ dwarf_begin_elf (Elf *elf, Dwarf_Cmd cmd, Elf_Scn *scngrp)
 
   result->elf = elf;
   result->alt_fd = -1;
+  result->dwp_fd = -1;
 
   /* Initialize the memory handling.  Initial blocks are allocated on first
      actual allocation.  */
diff --git a/libdw/dwarf_cu_dwp_section_info.c b/libdw/dwarf_cu_dwp_section_info.c
index 4a4eac8c..298f36f9 100644
--- a/libdw/dwarf_cu_dwp_section_info.c
+++ b/libdw/dwarf_cu_dwp_section_info.c
@@ -340,6 +340,25 @@ __libdw_dwp_find_unit (Dwarf *dbg, bool debug_types, Dwarf_Off off,
 				   abbrev_offsetp, NULL);
 }
 
+Dwarf_CU *
+internal_function
+__libdw_dwp_findcu_id (Dwarf *dbg, uint64_t unit_id8)
+{
+  Dwarf_Package_Index *index = __libdw_package_index (dbg, false);
+  uint32_t unit_row;
+  Dwarf_Off offset;
+  Dwarf_CU *cu;
+  if (__libdw_dwp_unit_row (index, unit_id8, &unit_row) == 0
+      && __libdw_dwp_section_info (index, unit_row, DW_SECT_INFO, &offset,
+				   NULL) == 0
+      && (cu = __libdw_findcu (dbg, offset, false)) != NULL
+      && cu->unit_type == DW_UT_split_compile
+      && cu->unit_id8 == unit_id8)
+    return cu;
+  else
+    return NULL;
+}
+
 int
 dwarf_cu_dwp_section_info (Dwarf_CU *cu, unsigned int section,
 			   Dwarf_Off *offsetp, Dwarf_Off *sizep)
diff --git a/libdw/dwarf_end.c b/libdw/dwarf_end.c
index b7f817d9..78224ddb 100644
--- a/libdw/dwarf_end.c
+++ b/libdw/dwarf_end.c
@@ -66,7 +66,9 @@ cu_free (void *arg)
 	  /* The fake_addr_cu might be shared, only release one.  */
 	  if (p->dbg->fake_addr_cu == p->split->dbg->fake_addr_cu)
 	    p->split->dbg->fake_addr_cu = NULL;
-	  INTUSE(dwarf_end) (p->split->dbg);
+	  /* There is only one DWP file. We free it later.  */
+	  if (p->split->dbg != p->dbg->dwp_dwarf)
+	    INTUSE(dwarf_end) (p->split->dbg);
 	}
     }
 }
@@ -147,6 +149,12 @@ dwarf_end (Dwarf *dwarf)
 	  close (dwarf->alt_fd);
 	}
 
+      if (dwarf->dwp_fd != -1)
+	{
+	  INTUSE(dwarf_end) (dwarf->dwp_dwarf);
+	  close (dwarf->dwp_fd);
+	}
+
       /* The cached path and dir we found the Dwarf ELF file in.  */
       free (dwarf->elfpath);
       free (dwarf->debugdir);
diff --git a/libdw/libdwP.h b/libdw/libdwP.h
index 7f8d69b5..54445886 100644
--- a/libdw/libdwP.h
+++ b/libdw/libdwP.h
@@ -180,6 +180,9 @@ struct Dwarf
   /* dwz alternate DWARF file.  */
   Dwarf *alt_dwarf;
 
+  /* DWARF package file.  */
+  Dwarf *dwp_dwarf;
+
   /* The section data.  */
   Elf_Data *sectiondata[IDX_last];
 
@@ -197,6 +200,9 @@ struct Dwarf
      close this file descriptor.  */
   int alt_fd;
 
+  /* File descriptor of DWARF package file.  */
+  int dwp_fd;
+
   /* Information for traversing the .debug_pubnames section.  This is
      an array and separately allocated with malloc.  */
   struct pubnames_s
@@ -716,6 +722,10 @@ extern int __libdw_dwp_find_unit (Dwarf *dbg, bool debug_types, Dwarf_Off off,
 				  Dwarf_Off *abbrev_offsetp)
      __nonnull_attribute__ (1, 7, 8) internal_function;
 
+/* Find the compilation unit in a DWARF package file with the given id.  */
+extern Dwarf_CU *__libdw_dwp_findcu_id (Dwarf *dbg, uint64_t unit_id8)
+     __nonnull_attribute__ (1) internal_function;
+
 /* Get abbreviation with given code.  */
 extern Dwarf_Abbrev *__libdw_findabbrev (struct Dwarf_CU *cu,
 					 unsigned int code)
@@ -1367,12 +1377,19 @@ __libdw_link_skel_split (Dwarf_CU *skel, Dwarf_CU *split)
 
   /* Get .debug_addr and addr_base greedy.
      We also need it for the fake addr cu.
-     There is only one per split debug.  */
+     This needs to be done for each split unit (one per .dwo file, or multiple
+     per .dwp file).  */
   Dwarf *dbg = skel->dbg;
   Dwarf *sdbg = split->dbg;
-  if (sdbg->sectiondata[IDX_debug_addr] == NULL
-      && dbg->sectiondata[IDX_debug_addr] != NULL)
+  if (dbg->sectiondata[IDX_debug_addr] != NULL
+      /* If this split file hasn't been linked yet...  */
+      && (sdbg->sectiondata[IDX_debug_addr] == NULL
+	  /* ... or it was linked to the same skeleton file for another
+	     unit...  */
+	  || (sdbg->sectiondata[IDX_debug_addr]
+	      == dbg->sectiondata[IDX_debug_addr])))
     {
+      /* ... then link the address information for this file and unit.  */
       sdbg->sectiondata[IDX_debug_addr]
 	= dbg->sectiondata[IDX_debug_addr];
       split->addr_base = __libdw_cu_addr_base (skel);
diff --git a/libdw/libdw_find_split_unit.c b/libdw/libdw_find_split_unit.c
index 533f8072..e1e78951 100644
--- a/libdw/libdw_find_split_unit.c
+++ b/libdw/libdw_find_split_unit.c
@@ -85,6 +85,67 @@ try_split_file (Dwarf_CU *cu, const char *dwo_path)
     }
 }
 
+static void
+try_dwp_file (Dwarf_CU *cu)
+{
+  if (cu->dbg->dwp_dwarf == NULL)
+    {
+      if (cu->dbg->elfpath != NULL)
+	{
+	  /* The DWARF 5 standard says "the package file is typically placed in
+	     the same directory as the application, and is given the same name
+	     with a '.dwp' extension".  */
+	  size_t elfpath_len = strlen (cu->dbg->elfpath);
+	  char *dwp_path = malloc (elfpath_len + 5);
+	  if (dwp_path == NULL)
+	    {
+	      __libdw_seterrno (DWARF_E_NOMEM);
+	      return;
+	    }
+	  memcpy (dwp_path, cu->dbg->elfpath, elfpath_len);
+	  strcpy (dwp_path + elfpath_len, ".dwp");
+	  int dwp_fd = open (dwp_path, O_RDONLY);
+	  free (dwp_path);
+	  if (dwp_fd != -1)
+	    {
+	      Dwarf *dwp_dwarf = dwarf_begin (dwp_fd, DWARF_C_READ);
+	      /* There's no way to know whether we got the correct file until
+		 we look up the unit, but it should at least be a dwp file.  */
+	      if (dwp_dwarf != NULL
+		  && (dwp_dwarf->sectiondata[IDX_debug_cu_index] != NULL
+		      || dwp_dwarf->sectiondata[IDX_debug_tu_index] != NULL))
+		{
+		  cu->dbg->dwp_dwarf = dwp_dwarf;
+		  cu->dbg->dwp_fd = dwp_fd;
+		}
+	      else
+		close (dwp_fd);
+	    }
+	}
+      if (cu->dbg->dwp_dwarf == NULL)
+	cu->dbg->dwp_dwarf = (Dwarf *) -1;
+    }
+
+  if (cu->dbg->dwp_dwarf != (Dwarf *) -1)
+    {
+      Dwarf_CU *split = __libdw_dwp_findcu_id (cu->dbg->dwp_dwarf,
+					       cu->unit_id8);
+      if (split != NULL)
+	{
+	  if (tsearch (split->dbg, &cu->dbg->split_tree,
+		       __libdw_finddbg_cb) == NULL)
+	    {
+	      /* Something went wrong.  Don't link.  */
+	      __libdw_seterrno (DWARF_E_NOMEM);
+	      return;
+	    }
+
+	  /* Link skeleton and split compile units.  */
+	  __libdw_link_skel_split (cu, split);
+	}
+    }
+}
+
 Dwarf_CU *
 internal_function
 __libdw_find_split_unit (Dwarf_CU *cu)
@@ -98,14 +159,18 @@ __libdw_find_split_unit (Dwarf_CU *cu)
      same id as the skeleton.  */
   if (cu->unit_type == DW_UT_skeleton)
     {
+      /* First, try the dwp file.  */
+      try_dwp_file (cu);
+
       Dwarf_Die cudie = CUDIE (cu);
       Dwarf_Attribute dwo_name;
-      /* It is fine if dwo_dir doesn't exists, but then dwo_name needs
-	 to be an absolute path.  */
-      if (dwarf_attr (&cudie, DW_AT_dwo_name, &dwo_name) != NULL
-	  || dwarf_attr (&cudie, DW_AT_GNU_dwo_name, &dwo_name) != NULL)
+      /* Try a dwo file.  It is fine if dwo_dir doesn't exist, but then
+	 dwo_name needs to be an absolute path.  */
+      if (cu->split == (Dwarf_CU *) -1
+	  && (dwarf_attr (&cudie, DW_AT_dwo_name, &dwo_name) != NULL
+	      || dwarf_attr (&cudie, DW_AT_GNU_dwo_name, &dwo_name) != NULL))
 	{
-	  /* First try the dwo file name in the same directory
+	  /* Try the dwo file name in the same directory
 	     as we found the skeleton file.  */
 	  const char *dwo_file = dwarf_formstring (&dwo_name);
 	  const char *debugdir = cu->dbg->debugdir;
-- 
2.43.0