From: Andrew Burgess <aburgess@redhat.com>
Date: Thu, 27 Nov 2025 17:08:56 +0000 (+0000)
Subject: gdb/dwarf: remove line_header parameter from dwarf2_decode_lines
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e4d4bb9f71d714f3c2fc1c0ddfa7d1897843e675;p=thirdparty%2Fbinutils-gdb.git

gdb/dwarf: remove line_header parameter from dwarf2_decode_lines

The function declaration for dwarf2_decode_lines is:

  void dwarf_decode_lines (struct line_header *lh, struct dwarf2_cu *cu,
                           unrelocated_addr lowpc, bool decode_mapping)

However, it is always the case that:

  lh == cu->line_header

I propose that we simplify the dwarf_decode_lines signature by
removing the line_header parameter.  The same is true for
dwarf_decode_lines_1, which is only called from dwarf_decode_lines.

I'm proposing this change because I was looking through the DWARF
code, trying to understand how symtabs are created, and this extra
complexity just makes things harder to understand: what is the
relationship between the line_header (LH) and dwarf2_cu (CU)
parameters?  When would we ever want to process a line_header other
than the one attached to CU? (answer: never, and we don't).  This
simplification makes things easier to understand (IMHO).
There should be no user visible changes after this commit.

Approved-By: Tom Tromey <tom@tromey.com>
---

diff --git a/gdb/dwarf2/line-program.c b/gdb/dwarf2/line-program.c
index 6670026799a..094f0dec806 100644
--- a/gdb/dwarf2/line-program.c
+++ b/gdb/dwarf2/line-program.c
@@ -481,12 +481,12 @@ lnp_state_machine::check_line_address (struct dwarf2_cu *cu,
 }
 
 /* Subroutine of dwarf_decode_lines to simplify it.
-   Process the line number information in LH.  */
+   Process the line number information in CU::line_header.  */
 
 static void
-dwarf_decode_lines_1 (struct line_header *lh, struct dwarf2_cu *cu,
-		      unrelocated_addr lowpc)
+dwarf_decode_lines_1 (struct dwarf2_cu *cu, unrelocated_addr lowpc)
 {
+  struct line_header *lh = cu->line_header;
   const gdb_byte *line_ptr, *extended_end;
   const gdb_byte *line_end;
   unsigned int bytes_read, extended_len;
@@ -694,11 +694,11 @@ dwarf_decode_lines_1 (struct line_header *lh, struct dwarf2_cu *cu,
 /* See dwarf2/line-program.h.  */
 
 void
-dwarf_decode_lines (struct line_header *lh, struct dwarf2_cu *cu,
-		    unrelocated_addr lowpc, bool decode_mapping)
+dwarf_decode_lines (struct dwarf2_cu *cu, unrelocated_addr lowpc,
+		    bool decode_mapping)
 {
   if (decode_mapping)
-    dwarf_decode_lines_1 (lh, cu, lowpc);
+    dwarf_decode_lines_1 (cu, lowpc);
 
   /* Make sure a symtab is created for every file, even files
      which contain only variables (i.e. no code with associated
@@ -706,7 +706,8 @@ dwarf_decode_lines (struct line_header *lh, struct dwarf2_cu *cu,
   buildsym_compunit *builder = cu->get_builder ();
   struct compunit_symtab *cust = builder->get_compunit_symtab ();
 
-  for (auto &fe : lh->file_names ())
+  struct line_header *lh = cu->line_header;
+  for (file_entry &fe : lh->file_names ())
     {
       dwarf2_start_subfile (cu, fe, *lh);
       subfile *sf = builder->get_current_subfile ();
diff --git a/gdb/dwarf2/line-program.h b/gdb/dwarf2/line-program.h
index 9b4e91c12ec..060b1ffbfbf 100644
--- a/gdb/dwarf2/line-program.h
+++ b/gdb/dwarf2/line-program.h
@@ -20,12 +20,7 @@
 #ifndef GDB_DWARF2_LINE_PROGRAM_H
 #define GDB_DWARF2_LINE_PROGRAM_H
 
-/* Decode the Line Number Program (LNP) for the given line_header
-   structure and CU.  The actual information extracted and the type
-   of structures created from the LNP depends on the value of PST.
-
-   FND holds the CU file name and directory, if known.
-   It is used for relative paths in the line table.
+/* Decode the Line Number Program (LNP) for CU::line_header.
 
    NOTE: It is important that psymtabs have the same file name (via
    strcmp) as the corresponding symtab.  Since the directory is not
@@ -40,8 +35,7 @@
    for its PC<->lines mapping information.  Otherwise only the filename
    table is read in.  */
 
-extern void dwarf_decode_lines (struct line_header *lh,
-				struct dwarf2_cu *cu,
+extern void dwarf_decode_lines (struct dwarf2_cu *cu,
 				unrelocated_addr lowpc, bool decode_mapping);
 
 #endif /* GDB_DWARF2_LINE_PROGRAM_H */
diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 4b706f654e0..5311016b257 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -6089,7 +6089,7 @@ handle_DW_AT_stmt_list (struct die_info *die, struct dwarf2_cu *cu,
      then there won't be any interesting code in the CU, but a check later on
      (in lnp_state_machine::check_line_address) will fail to properly exclude
      an entry that was removed via --gc-sections.  */
-  dwarf_decode_lines (cu->line_header, cu, lowpc, decode_mapping && have_code);
+  dwarf_decode_lines (cu, lowpc, decode_mapping && have_code);
 }
 
 /* Process DW_TAG_compile_unit or DW_TAG_partial_unit.  */