[llvm-bugs] [Bug 35248] New: LLD .map files: Request more info for "<internal>:(.rodata)"

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=35248

            Bug ID: 35248
           Summary: LLD .map files: Request more info for
                    "<internal>:(.rodata)"
           Product: lld
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: ELF
          Assignee: unassignedbugs at nondot.org
          Reporter: huangs at google.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 19387
  --> https://bugs.llvm.org/attachment.cgi?id=19387&action=edit
Sample .map outputs and script + sources to generate them.

LLD's generated .map file provides no semantic information on merged data in
.rodata section.  In particular, merged strings are not distinguished from
other data; everything is labelled as "<internal>:(.rodata)".

The missing information is useful for tools that parse .map file to annotate
executable bytes to source.  An example is Chrome's Supersize too (that I'm
working on):
https://github.com/webrtc-uwp/chromium-tools/blob/master/binary_size/README.md

Comparison with other linkers:

LD .map files annotates  .rodata section names from the original .o files, 
.rodata.cst4   0x0000000000400ad0        0x4
/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../x86_64-linux-gnu/crt1.o
                0x0000000000400ad0                _IO_stdin_used
 *fill*         0x0000000000400ad4        0x4 
 .rodata.cst8   0x0000000000400ad8        0x8 a.o
 .rodata.str1.1
                0x0000000000400ae0       0x3e a.o
                                         0x44 (size before relaxing)


GOLD .map files provides less info, but identifies the type ("** merge
constants" vs. "** mege strings"), e.g.:
.rodata         0x0000000000400af0       0x60
 ** merge constants
                0x0000000000400af0        0x4
 ** merge constants
                0x0000000000400af8        0x8
 ** merge strings
                0x0000000000400b00       0x44


Meanwhile, LLD .map files only has "<internal>:(.rodata)", e.g.:
00000000002002e8 0000000000000060     8 .rodata
00000000002002e8 0000000000000004     4         <internal>:(.rodata)
00000000002002f0 0000000000000008     8         <internal>:(.rodata)
00000000002002f8 0000000000000044     1         <internal>:(.rodata)
0000000000200340 0000000000000008     8         b.o:(.rodata)
0000000000200340 0000000000000008     0                 b


The attached .zip file contains examples to generate the above ('genall'
generates the .map files, and need to be tweaked to get proper paths).

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