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  1. 06 Nov, 2013 1 commit
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  9. 31 Oct, 2013 2 commits
    • Russ Cox's avatar
      cmd/5l, runtime: fix divide for profiling tracebacks on ARM · 2c98a3bc
      Russ Cox authored 
      Two bugs:
1. The first iteration of the traceback always uses LR when provided,
which it is (only) during a profiling signal, but in fact LR is correct
only if the stack frame has not been allocated yet. Otherwise an
intervening call may have changed LR, and the saved copy in the stack
frame should be used. Fix in traceback_arm.c.

2. The division runtime call adds 8 bytes to the stack. In order to
keep the traceback routines happy, it must copy the saved LR into
the new 0(SP). Change

        SUB $8, SP

into

        MOVW    0(SP), R11 // r11 is temporary, for use by linker
        MOVW.W  R11, -8(SP)

to update SP and 0(SP) atomically, so that the traceback always
sees a saved LR at 0(SP).

Fixes #6681.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/19910044
      2c98a3bc
    • Russ Cox's avatar
      undo CL 19810043 / 352f3b7c9664 · b88148b9
      Russ Cox authored 
      The CL causes misc/cgo/test to fail randomly.
I suspect that the problem is the use of a division instruction
in usleep, which can be called while trying to acquire an m
and therefore cannot store the denominator in m.
The solution to that would be to rewrite the code to use a
magic multiply instead of a divide, but now we're getting
pretty far off the original code.

Go back to the original in preparation for a different,
less efficient but simpler fix.

««« original CL description
cmd/5l, runtime: make ARM integer division profiler-friendly

The implementation of division constructed non-standard
stack frames that could not be handled by the traceback
routines.

CL 13239052 left the frames non-standard but fixed them
for the specific case of a divide-by-zero panic.
A profiling signal can arrive at any time, so that fix
is not sufficient.

Change the division to store the extra argument in the M struct
instead of in a new stack slot. That keeps the frames bog standard
at all times.

Also fix a related bug in the traceback code: when starting
a traceback, the LR register should be ignored if the current
function has already allocated its stack frame and saved the
original LR on the stack. The stack copy should be used, as the
LR register may have been modified.

Combined, these make the torture test from issue 6681 pass.

Fixes #6681.

R=golang-dev, r, josharian
CC=golang-dev
https://golang.org/cl/19810043
»»»

TBR=r
CC=golang-dev
https://golang.org/cl/20350043
      b88148b9
  11. 30 Oct, 2013 6 commits
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