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cmd/5l, cmd/6l, cmd/8l: fix nacl binary corruption bug

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NaCl requires the addition of a 32-byte "halt sled" at the end
of the text segment. This means that segtext.len is actually
32 bytes shorter than reality. The computation of the file offset
of the end of the data segment did not take this 32 bytes into
account, so if len and len+32 rounded up (by 64k) to different
values, the symbol table overwrote the last page of the data
segment.

The last page of the data segment is usually the C .string
symbols, which contain the strings used in error prints
by the runtime. So when this happens, your program
probably crashes, and then when it does, you get binary
garbage instead of all the usual prints.

The chance of hitting this with a randomly sized text segment
is 32 in 65536, or 1 in 2048.

If you add or remove ANY code while trying to debug this
problem, you're overwhelmingly likely to bump the text
segment one way or the other and make the bug disappear.

Correct all the computations to use segdata.fileoff+segdata.filelen
instead of trying to rederive segdata.fileoff.

This fixes the failure during the nacl/amd64p32 build.

TBR=iant
CC=golang-codereviews
https://golang.org/cl/135050043
This commit is contained in:
Russ Cox 2014-08-27 22:53:28 -04:00
parent f9b9ecc5ee
commit a9b2651ade
3 changed files with 10 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
src/cmd/5l/asm.c
View File

@ -599,10 +599,10 @@ asmb(void)
if(iself)
goto ElfSym;
case Hplan9:
symo = HEADR+segtext.len+segdata.filelen;
symo = segdata.fileoff+segdata.filelen;
break;
ElfSym:
symo = rnd(HEADR+segtext.filelen, INITRND)+rnd(HEADR+segrodata.filelen, INITRND)+segdata.filelen;
symo = segdata.fileoff+segdata.filelen;
symo = rnd(symo, INITRND);
break;
}

8
src/cmd/6l/asm.c
View File

@ -698,10 +698,10 @@ asmb(void)
case Hplan9:
case Helf:
debug['s'] = 1;
symo = HEADR+segtext.len+segdata.filelen;
symo = segdata.fileoff+segdata.filelen;
break;
case Hdarwin:
symo = rnd(HEADR+segtext.len, INITRND)+rnd(segdata.filelen, INITRND)+machlink;
symo = segdata.fileoff+rnd(segdata.filelen, INITRND)+machlink;
break;
case Hlinux:
case Hfreebsd:
@ -710,11 +710,11 @@ asmb(void)
case Hdragonfly:
case Hsolaris:
case Hnacl:
symo = rnd(HEADR+segtext.len, INITRND)+rnd(segrodata.len, INITRND)+segdata.filelen;
symo = segdata.fileoff+segdata.filelen;
symo = rnd(symo, INITRND);
break;
case Hwindows:
symo = rnd(HEADR+segtext.filelen, PEFILEALIGN)+segdata.filelen;
symo = segdata.fileoff+segdata.filelen;
symo = rnd(symo, PEFILEALIGN);
break;
}

8
src/cmd/8l/asm.c
View File

@ -619,17 +619,17 @@ asmb(void)
if(iself)
goto Elfsym;
case Hplan9:
symo = HEADR+segtext.filelen+segdata.filelen;
symo = segdata.fileoff+segdata.filelen;
break;
case Hdarwin:
symo = rnd(HEADR+segtext.filelen, INITRND)+rnd(segdata.filelen, INITRND)+machlink;
symo = segdata.fileoff+rnd(segdata.filelen, INITRND)+machlink;
break;
Elfsym:
symo = rnd(HEADR+segtext.filelen, INITRND)+rnd(HEADR+segrodata.filelen, INITRND)+segdata.filelen;
symo = segdata.fileoff+segdata.filelen;
symo = rnd(symo, INITRND);
break;
case Hwindows:
symo = rnd(HEADR+segtext.filelen, PEFILEALIGN)+segdata.filelen;
symo = segdata.fileoff+segdata.filelen;
symo = rnd(symo, PEFILEALIGN);
break;
}