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cmd/ld: fix off-by-one error in DWARF .debug_line transcription

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The liblink refactor changed the DWARF .debug_line flow control. The mapping was off by one pcline entry. The fix here preserves pc until it can be compared to pcline.pc.

Sample dwarfdump .debug_line output for main.main from the program in issue 7351, before liblink (correct):

0x0000003c: 00 Extended: <9> 02 DW_LNE_set_address( 0x0000000000002000 )
0x00000047: 03 DW_LNS_advance_line( 6 )
0x00000049: 01 DW_LNS_copy
            0x0000000000002000      1      7      0 is_stmt

0x0000004a: 8b address += 21,  line += 1
            0x0000000000002021      1      8      0 is_stmt

0x0000004b: 02 DW_LNS_advance_pc( 153 )
0x0000004e: 03 DW_LNS_advance_line( 1 )
0x00000050: 01 DW_LNS_copy
            0x00000000000020ba      1      9      0 is_stmt

After liblink (off by one entry):

0x00001bbf: 00 Extended: <9> 02 DW_LNE_set_address( 0x0000000000002000 )
0x00001bca: 02 DW_LNS_advance_pc( 33 )
0x00001bcc: 03 DW_LNS_advance_line( 6 )
0x00001bce: 01 DW_LNS_copy
            0x0000000000002021      1      7      0 is_stmt

0x00001bcf: 02 DW_LNS_advance_pc( 153 )
0x00001bd2: 03 DW_LNS_advance_line( 1 )
0x00001bd4: 01 DW_LNS_copy
            0x00000000000020ba      1      8      0 is_stmt

0x00001bd5: 02 DW_LNS_advance_pc( 153 )
0x00001bd8: 03 DW_LNS_advance_line( 1 )
0x00001bda: 01 DW_LNS_copy
            0x0000000000002153      1      9      0 is_stmt

After this CL (the line 9 pc offset changed due to intervening compiler changes):

0x00001d07: 00 Extended: <9> 02 DW_LNE_set_address( 0x0000000000002000 )
0x00001d12: 03 DW_LNS_advance_line( 6 )
0x00001d14: 01 DW_LNS_copy
            0x0000000000002000      1      7      0 is_stmt

0x00001d15: 8b address += 21,  line += 1
            0x0000000000002021      1      8      0 is_stmt

0x00001d16: 02 DW_LNS_advance_pc( 189 )
0x00001d19: 03 DW_LNS_advance_line( 1 )
0x00001d1b: 01 DW_LNS_copy
            0x00000000000020de      1      9      0 is_stmt

Fixes #7351.

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/66290043
This commit is contained in:
Josh Bleecher Snyder 2014-02-20 09:06:32 -08:00
parent 58a9268f26
commit 15ec569ba9
1 changed files with 10 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
src/cmd/ld/dwarf.c
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@ -1590,29 +1590,30 @@ writelines(void)
pciterinit(&pcfile, &s->pcln->pcfile); pciterinit(&pcfile, &s->pcln->pcfile);
pciterinit(&pcline, &s->pcln->pcline); pciterinit(&pcline, &s->pcln->pcline);
epc = pc;
while(!pcfile.done && !pcline.done) { while(!pcfile.done && !pcline.done) {
if(pc - s->value >= pcfile.nextpc) { if(epc - s->value >= pcfile.nextpc) {
pciternext(&pcfile); pciternext(&pcfile);
continue; continue;
} }
if(pc - s->value >= pcline.nextpc) { if(epc - s->value >= pcline.nextpc) {
pciternext(&pcline); pciternext(&pcline);
continue; continue;
} }
if(pcfile.nextpc < pcline.nextpc)
epc = pcfile.nextpc;
else
epc = pcline.nextpc;
epc += s->value;
if(file != pcfile.value) { if(file != pcfile.value) {
cput(DW_LNS_set_file); cput(DW_LNS_set_file);
uleb128put(pcfile.value); uleb128put(pcfile.value);
file = pcfile.value; file = pcfile.value;
} }
putpclcdelta(epc - pc, pcline.value - line); putpclcdelta(s->value + pcline.pc - pc, pcline.value - line);
pc = epc; pc = epc;
if(pcfile.nextpc < pcline.nextpc)
epc = pcfile.nextpc;
else
epc = pcline.nextpc;
epc += s->value;
line = pcline.value; line = pcline.value;
} }