NetBSD Problem Report #58969

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Date: Tue,  7 Jan 2025 06:08:12 +0000 (UTC)
From: campbell+netbsd@mumble.net
Reply-To: campbell+netbsd@mumble.net
To: gnats-bugs@NetBSD.org
Subject: use of alloca is warning, not error, with -std=c11
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>Number:         58969
>Category:       toolchain
>Synopsis:       use of alloca is warning, not error, with -std=c11
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    toolchain-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Jan 07 06:10:00 +0000 2025
>Last-Modified:  Mon Jan 13 15:45:02 +0000 2025
>Originator:     Taylor R Campbell
>Release:        current
>Organization:
The NetBSD Foundalloca
>Environment:
>Description:
While experimenting with switching the build to -std=c11 (https://mail-index.netbsd.org/tech-kern/2025/01/05/msg029919.html), I saw warnings fly by like this:

/home/riastradh/netbsd/current/obj.riscv/tooldir/bin/../lib/gcc/riscv64--netbsd/12.4.0/../../../../riscv64--netbsd/bin/ld: /home/riastradh/netbsd/current/src/../obj.riscv/destdir.riscv/lib/libc.so: warning: Warning: reference to the libc supplied alloca(3); this most likely will not work. Please use the compiler provided version of alloca(3), by supplying the appropriate compiler flags (e.g. -std=gnu99).

We can easily address these by using -std=gnu11 for the handful of files that use alloca, like execlp.c, but this has to be a build error so we don't accidentally miss the warning scrolling past in build output.
>How-To-Repeat:
1. change -std=gnu99 to -std=c11 in share/mk/bsd.sys.mk
2. build libc and anything that uses it
>Fix:
Yes, please!

>Audit-Trail:
From: matthew green <mrg@eterna23.net>
To: gnats-bugs@netbsd.org
Cc: toolchain-manager@netbsd.org, gnats-admin@netbsd.org,
    netbsd-bugs@netbsd.org
Subject: re: toolchain/58969: use of alloca is warning, not error, with -std=c11
Date: Tue, 07 Jan 2025 18:31:04 +1100

 FWIW, it's a link error on arm64.

 is it not one on riscv*?

From: =?UTF-8?Q?J=C3=B6rg_Sonnenberger?= <joerg@bec.de>
To: gnats-bugs@netbsd.org, toolchain-manager@netbsd.org,
 gnats-admin@netbsd.org, netbsd-bugs@netbsd.org
Cc: 
Subject: Re: toolchain/58969: use of alloca is warning, not error, with
 -std=c11
Date: Tue, 7 Jan 2025 11:17:21 +0100

 On 1/7/25 7:10 AM, campbell+netbsd@mumble.net wrote:
 > While experimenting with switching the build to -std=c11 (https://mail-index.netbsd.org/tech-kern/2025/01/05/msg029919.html), I saw warnings fly by like this:
 > 
 > /home/riastradh/netbsd/current/obj.riscv/tooldir/bin/../lib/gcc/riscv64--netbsd/12.4.0/../../../../riscv64--netbsd/bin/ld: /home/riastradh/netbsd/current/src/../obj.riscv/destdir.riscv/lib/libc.so: warning: Warning: reference to the libc supplied alloca(3); this most likely will not work. Please use the compiler provided version of alloca(3), by supplying the appropriate compiler flags (e.g. -std=gnu99).

 AFAICT there are bugs around per-symbol linker warnings in GNU ld where 
 the warning is shown for dynamic libraries without anything in the 
 current object files ever using them.

 Joerg

From: Taylor R Campbell <campbell@mumble.net>
To: =?UTF-8?Q?J=C3=B6rg_Sonnenberger?= <joerg@bec.de>
Cc: gnats-bugs@netbsd.org, toolchain-manager@netbsd.org,
	gnats-admin@netbsd.org, netbsd-bugs@netbsd.org
Subject: Re: toolchain/58969: use of alloca is warning, not error, with
	-std=c11
Date: Tue, 7 Jan 2025 11:45:08 +0000

 > Date: Tue, 7 Jan 2025 11:17:21 +0100
 > From: J=F6rg Sonnenberger <joerg@bec.de>
 >=20
 > On 1/7/25 7:10 AM, campbell+netbsd@mumble.net wrote:
 > > While experimenting with switching the build to -std=3Dc11 (https://mai=
 l-index.netbsd.org/tech-kern/2025/01/05/msg029919.html), I saw warnings fly=
  by like this:
 > >=20
 > > /home/riastradh/netbsd/current/obj.riscv/tooldir/bin/../lib/gcc/riscv64=
 --netbsd/12.4.0/../../../../riscv64--netbsd/bin/ld: /home/riastradh/netbsd/=
 current/src/../obj.riscv/destdir.riscv/lib/libc.so: warning: Warning: refer=
 ence to the libc supplied alloca(3); this most likely will not work. Please=
  use the compiler provided version of alloca(3), by supplying the appropria=
 te compiler flags (e.g. -std=3Dgnu99).
 >=20
 > AFAICT there are bugs around per-symbol linker warnings in GNU ld where=20
 > the warning is shown for dynamic libraries without anything in the=20
 > current object files ever using them.

 In this case, the warning is legitimate, because the files in libc
 that _do_ use alloca -- execl.c, execle.c, execlp.c, and execvp.c --
 need to be built with -std=3Dgnu* in order to expose the real alloca,
 not -std=3Dc* which gives the broken stub reference, so compiling them
 with -std=3Dc11 broke them.

 We need to make this mistake a build-breaking error, not a scroll-by
 warning.

From: "Taylor R Campbell" <riastradh@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/58969 CVS commit: src
Date: Mon, 13 Jan 2025 15:40:18 +0000

 Module Name:	src
 Committed By:	riastradh
 Date:		Mon Jan 13 15:40:18 UTC 2025

 Modified Files:
 	src/share/mk: bsd.sys.mk
 	src/sys/conf: Makefile.kern.inc

 Log Message:
 Switch from -std=gnu99 to -std=gnu11 by default.

 This is needed for newer language syntax like u"foo" for UTF-16
 string literals in UEFI.

 As proposed on tech-kern:

 https://mail-index.netbsd.org/tech-kern/2025/01/05/msg029919.html

 Some commentators requested -std=c11 instead of -std=gnu11, but that
 requires additional work -- some of it is a matter of providing asm
 and typeof as aliases for __asm__ and __typeof__, but there's other
 issues that need to be resolved too like PR toolchain/58969: use of
 alloca is warning, not error, with -std=c11.  This is a smaller
 incremental change.

 PR toolchain/58962: clang build broken by C11 features with -std=gnu99


 To generate a diff of this commit:
 cvs rdiff -u -r1.316 -r1.317 src/share/mk/bsd.sys.mk
 cvs rdiff -u -r1.301 -r1.302 src/sys/conf/Makefile.kern.inc

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

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