libdw, readelf: Read inlining info in NVIDIA extended line map

As of CUDA 11.2, NVIDIA added extensions to the line map section
of CUDA binaries to represent inlined functions. These extensions
include

 - two new fields in a line table row to represent inline
   information: context, and functionname,

 - two new DWARF extended opcodes: DW_LNE_NVIDIA_inlined_call,
   DW_LNE_NVIDIA_set_function_name,

 - an additional word in the line table header that indicates
   the offset in the .debug_str function where the function
   names for this line table begin, and

A line table row for an inlined function contains a non-zero "context"
value. The “context” field indicates the index of the line table row
that serves as the call site for an inlined context.

The "functionname" field in a line table row is only meaningful if the
"context" field of the row is non-zero. A meaningful "functionname"
field contains an index into the .debug_str section relative to the
base offset established in the line table header; the position in the
.debug_str section indicates the name of the inlined function.

These extensions resemble the proposed DWARF extensions
(http://dwarfstd.org/ShowIssue.php?issue=140906.1) by Cary Coutant,
but are not identical.

This commit integrates support for handling NVIDIA's extended line
maps into elfutil's libdw library, by adding two functions
dwarf_linecontext and dwarf_linefunctionname, and the readelf
--debug-dump=line command line utility.

Signed-off-by: John M Mellor-Crummey <johnmc@rice.edu>
Signed-off-by: Mark Wielaard <mark@klomp.org>

2 files changed, 68 insertions, 0 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 316bcb6d..05b2522d 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,9 @@
+2021-10-20  John M Mellor-Crummey  <johnmc@rice.edu>
+
+	* readelf.c (print_debug_line_section): Try to read
+	debug_str_offset if available.  Handle DW_LNE_NVIDIA_inlined_call
+	and DW_LNE_NVIDIA_set_function_name.
+
 2021-10-06  Mark Wielaard  <mark@klomp.org>
 
 	* elflint.c (check_sections): Don't dereference databits if bad.
diff --git a/src/readelf.c b/src/readelf.c
index 3a199068..c10038e3 100644
--- a/src/readelf.c
+++ b/src/readelf.c
@@ -8478,6 +8478,8 @@ print_debug_line_section (Dwfl_Module *dwflmod, Ebl *ebl, GElf_Ehdr *ehdr,
 	  header_length = read_8ubyte_unaligned_inc (dbg, linep);
 	}
 
+      const unsigned char *header_start = linep;
+
       /* Next the minimum instruction length.  */
       if ((size_t) (lineendp - linep) < 1)
 	goto invalid_data;
@@ -8761,6 +8763,13 @@ print_debug_line_section (Dwfl_Module *dwflmod, Ebl *ebl, GElf_Ehdr *ehdr,
 	  ++linep;
 	}
 
+      unsigned int debug_str_offset = 0;
+      if (unlikely (linep == header_start + header_length - 4))
+	{
+	  /* CUBINs contain an unsigned 4-byte offset */
+	  debug_str_offset = read_4ubyte_unaligned_inc (dbg, linep);
+	}
+
       if (linep == lineendp)
 	{
 	  puts (_("\nNo line number statements."));
@@ -8909,6 +8918,59 @@ print_debug_line_section (Dwfl_Module *dwflmod, Ebl *ebl, GElf_Ehdr *ehdr,
 		  printf (_(" set discriminator to %u\n"), u128);
 		  break;
 
+		case DW_LNE_NVIDIA_inlined_call:
+		  {
+		    if (unlikely (linep >= lineendp))
+		      goto invalid_data;
+
+		    unsigned int context;
+		    get_uleb128 (context, linep, lineendp);
+
+		    if (unlikely (linep >= lineendp))
+		      goto invalid_data;
+
+		    unsigned int function_name;
+		    get_uleb128 (function_name, linep, lineendp);
+		    function_name += debug_str_offset;
+
+		    Elf_Data *str_data = dbg->sectiondata[IDX_debug_str];
+		    char *function_str;
+		    if (str_data == NULL || function_name >= str_data->d_size
+			|| memchr (str_data->d_buf + function_name, '\0',
+				   str_data->d_size - function_name) == NULL)
+		      function_str = "???";
+		    else
+		      function_str = (char *) str_data->d_buf + function_name;
+
+		    printf (_(" set inlined context %u,"
+		              " function name %s (0x%x)\n"),
+			    context, function_str, function_name);
+		    break;
+		  }
+
+		case DW_LNE_NVIDIA_set_function_name:
+		  {
+		    if (unlikely (linep >= lineendp))
+		      goto invalid_data;
+
+		    unsigned int function_name;
+		    get_uleb128 (function_name, linep, lineendp);
+		    function_name += debug_str_offset;
+
+		    Elf_Data *str_data = dbg->sectiondata[IDX_debug_str];
+		    char *function_str;
+		    if (str_data == NULL || function_name >= str_data->d_size
+			|| memchr (str_data->d_buf + function_name, '\0',
+				   str_data->d_size - function_name) == NULL)
+		      function_str = "???";
+		    else
+		      function_str = (char *) str_data->d_buf + function_name;
+
+		    printf (_(" set function name %s (0x%x)\n"),
+			    function_str, function_name);
+		  }
+		  break;
+
 		default:
 		  /* Unknown, ignore it.  */
 		  puts (_(" unknown opcode"));