code review 9103044: cmd/ld: fix another unsigned value causing bugs on Plan 9

cmd/ld: fix another unsigned value causing bugs on Plan 9
"The usual conversions" bite again.

[r, 2013-05-01 22:40:39]

Hello golang-dev@googlegroups.com,

I'd like you to review this change to
https://code.google.com/p/go

[rsc, 2013-05-01 23:56:33]

LGTM

I just realized it must be a bug in 8c and logged in to find you'd already
gotten there. Would be nice if 8c implemented the real rules, but that's for
another day.

https://codereview.appspot.com/9103044/diff/1/src/cmd/ld/data.c
File src/cmd/ld/data.c (right):

https://codereview.appspot.com/9103044/diff/1/src/cmd/ld/data.c#newcode250
src/cmd/ld/data.c:250: o += r->add - (s->value + r->off + (int32)r->siz);
// NOTE: The (int32) cast on the next line works around a bug in Plan 9's 8c
compiler.
// The expression s->value + r->off + r->siz is int32 + int32 + uchar,
// and Plan 9 8c incorrectly treats the expression as type uint32 instead of
int32,
// causing incorrect values when sign extended for adding to o.
// The bug only occurs on Plan 9, because this C program is compiled by the
// standard host compiler (gcc on most other systems).

[r, 2013-05-02 00:02:17]

*** Submitted as https://code.google.com/p/go/source/detail?r=9cd38a5658f3 ***

cmd/ld: fix another unsigned value causing bugs on Plan 9
"The usual conversions" bite again.

R=golang-dev, rsc
CC=golang-dev
https://codereview.appspot.com/9103044