On Thu, Sep 10, 2020 at 01:16:57PM +0200, Jakub Jelinek via Gcc-patches wrote:
> As for the test assembly, I'd say we should take
> #define F void foo (void) {}
> F
> compile it with
> gcc -S -O2 -g1 -dA -gno-as-loc-support -fno-merge-debug-strings
> remove .cfi_* directives, remove the ret instruction, change @function
> and @progbits to %function and %progbits, change .uleb128 to just .byte,
> I think all the values should be small enough, maybe change .value to
> .2byte and .long to .4byte (whatever is most portable across different
> arches and gas versions), simplify (shorten) strings and adjust
> sizes, and do something with the .quad directives, that is dependent on
> the address size, perhaps just take those attributes out and adjust
> .debug_abbrev? Finally, remove all comments (emit them in the first case
> just to better understand the debug info).
I'm afraid it is hard to avoid the .quad or .8byte.
Here is a 64-bit address version that assembles fine by both x86_64 and
aarch64 as.
Unfortunately doesn't fail with broken gas versions with -gdwarf-2 without
the nop, so we'll need at least a nop in there.
Fortunately gcc/configure.ac already determines the right nop insn for the
target, in $insn.
So I guess what we want next is have the 32-bit version of this with .4byte
instead of .8byte and just let's try to assemble both versions, first
without -gdwarf-2 and the one that succeeds assemble again with -gdwarf-2
and check for the duplicate .debug_line sections error.
What do you think?
.file "a.c"
.text
.Ltext0:
.p2align 4
.globl foo
.type foo, %function
foo:
.LFB0:
.LM1:
nop
.LM2:
.LFE0:
.size foo, .-foo
.Letext0:
.section .debug_info,"",%progbits
.Ldebug_info0:
.4byte 0x46
.2byte 0x4
.4byte .Ldebug_abbrev0
.byte 0x8
.byte 0x1
.ascii "GNU C17\0"
.byte 0xc
.ascii "a.c\0"
.ascii "/\0"
.8byte .Ltext0
.8byte .Letext0-.Ltext0
.4byte .Ldebug_line0
.byte 0x2
.ascii "foo\0"
.byte 0x1
.byte 0x2
.byte 0x1
.8byte .LFB0
.8byte .LFE0-.LFB0
.byte 0x1
.byte 0x9c
.byte 0
.section .debug_abbrev,"",%progbits
.Ldebug_abbrev0:
.byte 0x1
.byte 0x11
.byte 0x1
.byte 0x25
.byte 0x8
.byte 0x13
.byte 0xb
.byte 0x3
.byte 0x8
.byte 0x1b
.byte 0x8
.byte 0x11
.byte 0x1
.byte 0x12
.byte 0x7
.byte 0x10
.byte 0x17
.byte 0
.byte 0
.byte 0x2
.byte 0x2e
.byte 0
.byte 0x3f
.byte 0x19
.byte 0x3
.byte 0x8
.byte 0x3a
.byte 0xb
.byte 0x3b
.byte 0xb
.byte 0x39
.byte 0xb
.byte 0x11
.byte 0x1
.byte 0x12
.byte 0x7
.byte 0x40
.byte 0x18
.byte 0
.byte 0
.byte 0
.section .debug_aranges,"",%progbits
.4byte 0x2c
.2byte 0x2
.4byte .Ldebug_info0
.byte 0x8
.byte 0
.2byte 0
.2byte 0
.8byte .Ltext0
.8byte .Letext0-.Ltext0
.8byte 0
.8byte 0
.section .debug_line,"",%progbits
.Ldebug_line0:
.4byte .LELT0-.LSLT0
.LSLT0:
.2byte 0x4
.4byte .LELTP0-.LASLTP0
.LASLTP0:
.byte 0x1
.byte 0x1
.byte 0x1
.byte 0xf6
.byte 0xf2
.byte 0xd
.byte 0
.byte 0x1
.byte 0x1
.byte 0x1
.byte 0x1
.byte 0
.byte 0
.byte 0
.byte 0x1
.byte 0
.byte 0
.byte 0x1
.byte 0
.ascii "a.c\0"
.byte 0
.byte 0
.byte 0
.byte 0
.LELTP0:
.byte 0
.byte 0x9
.byte 0x2
.8byte .LM1
.byte 0x18
.byte 0x5
.byte 0x1
.byte 0
.byte 0x9
.byte 0x2
.8byte .LM2
.byte 0x1
.byte 0x5
.byte 0x1
.byte 0
.byte 0x9
.byte 0x2
.8byte .Letext0
.byte 0
.byte 0x1
.byte 0x1
.LELT0:
.section .debug_str,"",%progbits
.ident "GCC"
Jakub
