Date: Sat, 9 Jan 2021 03:05:48 +0100 From: Mateusz Guzik <mjguzik@gmail.com> To: Bryan Drewery <bdrewery@freebsd.org> Cc: src-committers@freebsd.org, dev-commits-src-all@freebsd.org, dev-commits-src-main@freebsd.org Subject: Re: git: f222a6b88614 - main - dtrace: Fix /"string" == NULL/ comparisons using an uninitialized value. Message-ID: <CAGudoHGKj1A4uY-5hy_UqfdzdtVO=dZMTjYCF3Z9P5MMm0nOqw@mail.gmail.com> In-Reply-To: <202101082237.108MbjU1068611@gitrepo.freebsd.org> References: <202101082237.108MbjU1068611@gitrepo.freebsd.org>
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tinderbox fails to build riscv kernels with:
In file included from
/usr/src/sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c:18434:
/usr/src/sys/cddl/dev/dtrace/riscv/dtrace_isa.c:155:13: error:
variable 'oldfp' is uninitialized when used here
[-Werror,-Wuninitialized]
if (fp == oldfp) {
^~~~~
/usr/src/sys/cddl/dev/dtrace/riscv/dtrace_isa.c:122:17: note:
initialize the variable 'oldfp' to silence this warning
uintptr_t oldfp;
^
= 0
1 error generated.
which stems from the Makefile change.
On 1/8/21, Bryan Drewery <bdrewery@freebsd.org> wrote:
> The branch main has been updated by bdrewery:
>
> URL:
> https://cgit.FreeBSD.org/src/commit/?id=f222a6b88614db13ae83c8110281e690d1381a4c
>
> commit f222a6b88614db13ae83c8110281e690d1381a4c
> Author: Bryan Drewery <bdrewery@FreeBSD.org>
> AuthorDate: 2020-12-18 17:58:03 +0000
> Commit: Bryan Drewery <bdrewery@FreeBSD.org>
> CommitDate: 2021-01-08 22:37:17 +0000
>
> dtrace: Fix /"string" == NULL/ comparisons using an uninitialized
> value.
>
> A test of this is funcs/tst.strtok.d which has this filter:
>
> BEGIN
> /(this->field = strtok(this->str, ",")) == NULL/
> {
> exit(1);
> }
> The test will randomly fail with exit status of 1 indicating that
> this->field
> was NULL even though printing it out shows it is not.
>
> This is compiled to the DTrace instruction set:
> // Pushed arguments not shown here
> // call strtok() and set result into %r1
> 07: 2f001f01 call DIF_SUBR(31), %r1 ! strtok
> // set thread local scalar this->field from %r1
> 08: 39050101 stls %r1, DT_VAR(1281) ! DT_VAR(1281) =
> "field"
> // Prepare for the == comparison
> // Set right side of %r2 to NULL
> 09: 25000102 setx DT_INTEGER[1], %r2 ! 0x0
> // string compare %r1 (strtok result) to %r2
> 10: 27010200 scmp %r1, %r2
>
> In this case only %r1 is loaded with a string limit set to lim1. %r2
> being
> NULL does not get loaded and does not set lim2. Then we call
> dtrace_strncmp()
> with MIN(lim1, lim2) resulting in passing 0 and comparing neither side.
> dtrace_strncmp() handles this case fine and it already has been while
> being lucky with what lim2 was [un]initialized as.
>
> Reviewed by: markj, Don Morris <dgmorris AT earthlink.net>
> Sponsored by: Dell EMC
> Differential Revision: https://reviews.freebsd.org/D27671
> ---
> sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c | 8 ++++++++
> sys/modules/dtrace/dtrace/Makefile | 1 -
> 2 files changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c
> b/sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c
> index 3d68a68ba819..b212185a4578 100644
> --- a/sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c
> +++ b/sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c
> @@ -6374,6 +6374,14 @@ dtrace_dif_emulate(dtrace_difo_t *difo,
> dtrace_mstate_t *mstate,
> uintptr_t s2 = regs[r2];
> size_t lim1, lim2;
>
> + /*
> + * If one of the strings is NULL then the limit becomes
> + * 0 which compares 0 characters in dtrace_strncmp()
> + * resulting in a false positive. dtrace_strncmp()
> + * treats a NULL as an empty 1-char string.
> + */
> + lim1 = lim2 = 1;
> +
> if (s1 != 0 &&
> !dtrace_strcanload(s1, sz, &lim1, mstate, vstate))
> break;
> diff --git a/sys/modules/dtrace/dtrace/Makefile
> b/sys/modules/dtrace/dtrace/Makefile
> index 80278fc83a32..55f9f4f66f36 100644
> --- a/sys/modules/dtrace/dtrace/Makefile
> +++ b/sys/modules/dtrace/dtrace/Makefile
> @@ -61,6 +61,5 @@ CFLAGS+= -include
> ${SYSDIR}/cddl/compat/opensolaris/sys/debug_compat.h
> CFLAGS.dtrace_asm.S+= -D_SYS_ERRNO_H_ -D_SYS_PARAM_H_ -DLOCORE
> CWARNFLAGS+= ${OPENZFS_CWARNFLAGS}
> CWARNFLAGS+= -Wno-parentheses
> -CWARNFLAGS+= -Wno-uninitialized
> CWARNFLAGS+= -Wno-cast-qual
> CWARNFLAGS+= -Wno-unused
>
--
Mateusz Guzik <mjguzik gmail.com>
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