On 12 August 2016 at 02:04, David Malcolm <dmalc...@redhat.com> wrote:
> I sometimes find myself scouring assembler output from the compiler
> and trying to figure out which instructions correspond to which
> lines of source code; I believe this is a common activity for some
> end-users.
Hi David,
I usually use gcc -g -Wa,-adhln to trace C source from the assembly.
I tried your example and it gave more or less a similar output (attached).
However the source mapping with your patch looks better.
Thanks,
Prathamesh
>
> The following patch adds a new -fasm-show-source option, which
> emits comments into the generated asm showing the pertinent
> line of source code, whenever it changes. It uses the same logic
> as debug_hooks->source_line for tracking this (for handling
> line-based breakpoints).
>
> An example can be seen in the invoke.texi part of the patch. As
> noted there, it's aimed at end-users, rather than gcc developers.
> The example shows a relatively short function; the option is
> likely to be much more useful for longer functions.
>
> I think it would further improve usability if this option were enabled
> by default when the final output is .s (either via -S, or by "-o foo.s").
> Ideas on how to implement that (in the driver) would be welcome - I
> started looking at the spec-handling code, but thought I'd post the
> idea here first, before diving in too deeply.
>
> Successfully bootstrapped®rtested on x86_64-pc-linux-gnu; adds
> 2 PASS results to gcc.sum.
>
> Thoughts? OK for trunk as-is?
>
> gcc/ChangeLog:
> * common.opt (fasm-show-source): New option.
> * doc/invoke.texi (Code Generation Options): Add
> -fasm-show-source.
> (-fasm-show-source): New item.
> * final.c (asm_show_source): New function.
> (final_scan_insn): Call asm_show_source.
>
> gcc/testsuite/ChangeLog:
> * gcc.dg/fasm-show-source-1.c: New test case.
> ---
> gcc/common.opt | 5 +++
> gcc/doc/invoke.texi | 71
> ++++++++++++++++++++++++++++++-
> gcc/final.c | 29 ++++++++++++-
> gcc/testsuite/gcc.dg/fasm-show-source-1.c | 15 +++++++
> 4 files changed, 117 insertions(+), 3 deletions(-)
> create mode 100644 gcc/testsuite/gcc.dg/fasm-show-source-1.c
>
> diff --git a/gcc/common.opt b/gcc/common.opt
> index 8a292ed..56ce513 100644
> --- a/gcc/common.opt
> +++ b/gcc/common.opt
> @@ -939,6 +939,11 @@ fargument-noalias-anything
> Common Ignore
> Does nothing. Preserved for backward compatibility.
>
> +fasm-show-source
> +Common Var(flag_asm_show_source)
> +Emit comments in the generated assembly code to show the source code
> +lines associated with the assembly instructions.
> +
> fsanitize=
> Common Driver Report Joined
> Select what to sanitize.
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index 22001f9..dc3d3ad 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -486,7 +486,8 @@ Objective-C and Objective-C++ Dialects}.
>
> @item Code Generation Options
> @xref{Code Gen Options,,Options for Code Generation Conventions}.
> -@gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
> +@gccoptlist{-fasm-show-source @gol
> +-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
> -ffixed-@var{reg} -fexceptions @gol
> -fnon-call-exceptions -fdelete-dead-exceptions -funwind-tables @gol
> -fasynchronous-unwind-tables @gol
> @@ -11153,6 +11154,74 @@ can figure out the other form by either removing
> @samp{no-} or adding
> it.
>
> @table @gcctabopt
> +@item -fasm-show-source
> +@opindex fasm-show-source
> +Emit comments in the generated assembly code to show the source code
> +lines associated with the assembly instructions. This option is
> +aimed at end-users who wish to better understand the relationship
> +between their source code and the generated machine code.
> +
> +The comments are of the form FILENAME:LINENUMBER:CONTENT OF LINE.
> +
> +For example, given this C source file:
> +
> +@smallexample
> +int test (int n)
> +@{
> + int i;
> + int total = 0;
> +
> + for (i = 0; i < n; i++)
> + total += i * i;
> +
> + return total;
> +@}
> +@end smallexample
> +
> +compiling to (x86_64) assembly via @option{-S} and emitting the result
> +direct to stdout via @option{-o} @option{-}
> +
> +@smallexample
> +gcc -S test.c -fasm-show-source -Os -o -
> +@end smallexample
> +
> +gives output similar to this, highlighting which instructions correspond
> +to the various parts of the loop:
> +
> +@smallexample
> + .file "test.c"
> + .text
> + .globl test
> + .type test, @@function
> +test:
> +.LFB0:
> + .cfi_startproc
> +# test.c:4: int total = 0;
> + xorl %eax, %eax
> +# test.c:6: for (i = 0; i < n; i++)
> + xorl %edx, %edx
> +.L2:
> +# test.c:6: for (i = 0; i < n; i++)
> + cmpl %edi, %edx
> + jge .L5
> +# test.c:7: total += i * i;
> + movl %edx, %ecx
> + imull %edx, %ecx
> +# test.c:6: for (i = 0; i < n; i++)
> + incl %edx
> +# test.c:7: total += i * i;
> + addl %ecx, %eax
> + jmp .L2
> +.L5:
> +# test.c:10: @}
> + ret
> + .cfi_endproc
> +.LFE0:
> + .size test, .-test
> + .ident "GCC: (GNU) 7.0.0 20160809 (experimental)"
> + .section .note.GNU-stack,"",@@progbits
> +@end smallexample
> +
> @item -fstack-reuse=@var{reuse-level}
> @opindex fstack_reuse
> This option controls stack space reuse for user declared local/auto variables
> diff --git a/gcc/final.c b/gcc/final.c
> index 5b04311..09bf0b7 100644
> --- a/gcc/final.c
> +++ b/gcc/final.c
> @@ -2140,6 +2140,27 @@ call_from_call_insn (rtx_call_insn *insn)
> return x;
> }
>
> +/* Implementation of -fasm-show-source.
> + Print a comment into the asm showing FILENAME, LINENUM, and the
> + corresponding source line, if available. */
> +
> +static void
> +asm_show_source (const char *filename, int linenum)
> +{
> + if (!filename)
> + return;
> +
> + int line_size;
> + const char *line = location_get_source_line (filename, linenum,
> &line_size);
> + if (!line)
> + return;
> +
> + fprintf (asm_out_file, "%s %s:%i: ", ASM_COMMENT_START, filename, linenum);
> + /* "line" is not 0-terminated, so we must use line_size. */
> + fwrite (line, 1, line_size, asm_out_file);
> + fputc ('\n', asm_out_file);
> +}
> +
> /* The final scan for one insn, INSN.
> Args are same as in `final', except that INSN
> is the insn being scanned.
> @@ -2563,8 +2584,12 @@ final_scan_insn (rtx_insn *insn, FILE *file, int
> optimize_p ATTRIBUTE_UNUSED,
> note in a row. */
> if (!DECL_IGNORED_P (current_function_decl)
> && notice_source_line (insn, &is_stmt))
> - (*debug_hooks->source_line) (last_linenum, last_filename,
> - last_discriminator, is_stmt);
> + {
> + if (flag_asm_show_source)
> + asm_show_source (last_filename, last_linenum);
> + (*debug_hooks->source_line) (last_linenum, last_filename,
> + last_discriminator, is_stmt);
> + }
>
> if (GET_CODE (body) == PARALLEL
> && GET_CODE (XVECEXP (body, 0, 0)) == ASM_INPUT)
> diff --git a/gcc/testsuite/gcc.dg/fasm-show-source-1.c
> b/gcc/testsuite/gcc.dg/fasm-show-source-1.c
> new file mode 100644
> index 0000000..3dd49e0
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/fasm-show-source-1.c
> @@ -0,0 +1,15 @@
> +/* Ensure that the generated asm contains FIXME */
> +/* { dg-options "-fasm-show-source" } */
> +
> +int test (int n)
> +{
> + int i;
> + int total = 0;
> +
> + for (i = 0; i < n; i++)
> + total += i * i;
> +
> + return total;
> +}
> +
> +/* { dg-final { scan-assembler "total = 0" } } */
> --
> 1.8.5.3
>
1 .file "foo.c"
2 .text
3 .Ltext0:
4 .section .text.unlikely,"ax",@progbits
5 .LCOLDB0:
6 .text
7 .LHOTB0:
8 .section .text.unlikely
9 .Ltext_cold0:
10 .text
11 .globl f
13 f:
14 .LFB0:
15 .file 1 "foo.c"
1:foo.c **** int f(int n)
2:foo.c **** {
16 .loc 1 2 0
17 .cfi_startproc
18 .LVL0:
19 .LBB2:
3:foo.c **** int total = 0;
4:foo.c **** for (int i = 0; i < n; i++)
20 .loc 1 4 0
21 0000 31D2 xorl %edx, %edx
22 .LBE2:
3:foo.c **** int total = 0;
23 .loc 1 3 0
24 0002 31C0 xorl %eax, %eax
25 .LVL1:
26 .L2:
27 .LBB3:
28 .loc 1 4 0 discriminator 1
29 0004 39FA cmpl %edi, %edx
30 0006 7D0B jge .L5
5:foo.c **** total += i * i;
31 .loc 1 5 0 discriminator 3
32 0008 89D1 movl %edx, %ecx
33 000a 0FAFCA imull %edx, %ecx
4:foo.c **** return total;
34 .loc 1 4 0 discriminator 3
35 000d FFC2 incl %edx
36 .LVL2:
37 .loc 1 5 0 discriminator 3
38 000f 01C8 addl %ecx, %eax
39 .LVL3:
40 0011 EBF1 jmp .L2
41 .L5:
42 .LBE3:
6:foo.c **** return total;
7:foo.c **** }
43 .loc 1 7 0
44 0013 C3 ret
45 .cfi_endproc
46 .LFE0:
48 .section .text.unlikely
49 .LCOLDE0:
50 .text
51 .LHOTE0:
52 .Letext0:
53 .section .text.unlikely
54 .Letext_cold0:
