Patchwork [Bug,1824853,NEW] 4.0.0-rc3 crashes with tcg/tcg.c:3952: tcg_gen_code: Assertion `s->gen_insn_end_off[num_insns] == off' failed

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Submitter Roman Zhuykov
Date April 15, 2019, 5:07 p.m.
Message ID <155534806981.13632.6401186723464432088.malonedeb@gac.canonical.com>
Download mbox | patch
Permalink /patch/773503/
State New
Headers show

Comments

Roman Zhuykov - April 15, 2019, 5:07 p.m.
Public bug reported:

I tried to bootstrap and regtested gcc trunk (gcc svn rev 270278,
datestamp 20190411) inside my arm64-gentoo installation under qemu-
system-aarch64.

Qemu version was 4.0.0-rc3 and -cpu cortex-a57. Qemu configured with
only --target-list=aarch64-softmmu,aarch64-linux-user and compiled using
gcc "version 5.5.0 20171010 (Ubuntu 5.5.0-12ubuntu1~16.04)".

Executable created from gcc/testsuite/gcc.target/aarch64/advsimd-
intrinsics/vldX.c compiled with -O2 crashed the whole qemu-system.

To investigate a bit I also manually run
~/gcc/inst/trunk/bin/gcc ~/gcc/src/trunk/gcc/testsuite/gcc.target/aarch64/advsimd-intrinsics/vldX.c
with different options like:
-O0 -lm -o d0.exe
-O1 -lm -o d1.exe
-O2 -lm -o d2.exe
-O0 -static -lm -o s0.exe
-O1 -static -lm -o s1.exe
-O2 -static -lm -o s2.exe

So, now I have 6 different arm64 executables created with different optimization levels. O0 and O1 versions run ok.
Three sN.exe static executables I've also tried in qemu user mode (with same -cpu), no issue in user mode.

And inside qemu-system I can see that
running "d2.exe" (attached) gives:
tcg/tcg.c:3952: tcg_gen_code: Assertion `s->gen_insn_end_off[num_insns] == off' failed.

And running "s2.exe" gives:
tcg/tcg.c:320: set_jmp_reset_offset: Assertion `s->tb_jmp_reset_offset[which] == off' failed.

It seems like this test is an counter-example for logic that
"tcg_ctx->nb_ops < 4000" implies tcg will fit into 16-bit signed size
(see tcg_op_buf_full comments).

Richard's changes in abebf92597186 and 9f754620651d were not enough, translation block must be smaller, or we have to find some proper way to bail out when buffer overflows.
I don't know why this situation is not caught by code_gen_highwater logic in tcg.c

I've also tried this "bail out" patch


But then running "d2.exe" just hangs the whole qemu-system. It seems
that when tcg_gen_code return -1 (like in highwater logic mentioned
before), we just re-call it again and again.

** Affects: qemu
     Importance: Undecided
         Status: New

** Attachment added: "d2.exe"
   https://bugs.launchpad.net/bugs/1824853/+attachment/5255996/+files/d2.exe
Roman Zhuykov - April 15, 2019, 5:09 p.m.
Also attaching static-compiled executable "s2.exe".

** Attachment added: "s2.exe"
   https://bugs.launchpad.net/qemu/+bug/1824853/+attachment/5256000/+files/s2.exe
Richard Henderson - April 16, 2019, 4:01 a.m.
Returning -1 does not help because all that signals that the buffer is full.
We then flush the buffer and try again, assuming the at the buffer will not fill.
Given that the buffer is usually many megabytes, this is reasonable.

We need something different to signal that the buffer is not full, but that
another offset has overflowed.

** Changed in: qemu
       Status: New => Confirmed

** Changed in: qemu
       Status: Confirmed => In Progress

** Changed in: qemu
     Assignee: (unassigned) => Richard Henderson (rth)
Richard Henderson - April 16, 2019, 8:36 a.m.
Patch set posted:
https://patchwork.ozlabs.org/project/qemu-devel/list/?series=102978
Roman Zhuykov - April 17, 2019, 11:26 a.m.
Richard, thank you for solving this so fast!
I certainly can confirm attached executables work fine for me on patched version.

I'll also re-run full gcc regtest a bit later, but it runs for a rather
long time, not sure this result will be important next week.

Hopefully, patchset will be included into 4 release.
Peter Maydell - April 17, 2019, 12:12 p.m.
Unfortunately the fix is too big for this point in the 4.0 release
cycle; it'll go into 4.1.

Patch

diff --git a/tcg/tcg.c b/tcg/tcg.c
--- a/tcg/tcg.c
+++ b/tcg/tcg.c
@@ -3949,7 +3949,8 @@  int tcg_gen_code(TCGContext *s, TranslationBlock *tb)
                 size_t off = tcg_current_code_size(s);
                 s->gen_insn_end_off[num_insns] = off;
                 /* Assert that we do not overflow our stored offset.  */
-                assert(s->gen_insn_end_off[num_insns] == off);
+                if (s->gen_insn_end_off[num_insns] != off)
+                  return -1;
             }
             num_insns++;
             for (i = 0; i < TARGET_INSN_START_WORDS; ++i) {