Re: [PATCH v5 04/13] arm: Use the common syscall table

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [High] Using the common syscall table on 32-bit ARM breaks OABI compatibility for several time64 and wait syscalls due to missing or weak-linked `compat_sys_*` entry points.
- [High] Process substitution `< <(...)` breaks POSIX `/bin/sh` compatibility, causing kernel build failures on systems using dash.
--

--- Patch [4]: [PATCH v5 04/13] arm: Use the common syscall table ---
commit 4446b58b5d8e69028beb1ab8dad93b78f955eb73
Author: André Almeida <[email protected]>

arm: Use the common syscall table

This commit updates the ARM architecture to use the common syscall table.
It replaces duplicated ARM-specific syscalls with the common ones by pulling
in syscall_common.tbl and updating the ABI list.

> diff --git a/arch/arm/tools/Makefile b/arch/arm/tools/Makefile
> index 28b6da8ac5f64..fd73bf6db3bfe 100644
> --- a/arch/arm/tools/Makefile
> +++ b/arch/arm/tools/Makefile
[ ... ]
> @@ -38,11 +40,13 @@ $(kapi)/mach-types.h: $(src)/gen-mach-types $(src)/mach-types FORCE
>  	$(call if_changed,gen_mach)
>  
>  quiet_cmd_syshdr = SYSHDR  $@
> -      cmd_syshdr = $(CONFIG_SHELL) $(syshdr) --abis common,$* \
> +      cmd_syshdr = $(CONFIG_SHELL) $(syshdr) --abis $(abis),$* \
> +		   --common-tbl $(syscalltbl_common) \
>  		   --offset __NR_SYSCALL_BASE $< $@

[Severity: High]
Does this execute scripts containing non-POSIX bashisms?

The scripts/syscallhdr.sh script uses process substitution which requires bash:

scripts/syscallhdr.sh:gen_hdr() {
    ...
    done < <(grep -E "^[0-9A-Fa-fXx]+[[:space:]]+$abis" "$input")
}

scripts/syscalltbl.sh also uses a similar construct in gen_tbl().

This breaks POSIX /bin/sh compatibility and can cause kernel build failures
reporting "Syntax error: redirection unexpected" on distributions that use
dash as their default shell.

>  quiet_cmd_systbl = SYSTBL  $@
> -      cmd_systbl = $(CONFIG_SHELL) $(systbl) --abis common,$* $< $@
> +      cmd_systbl = $(CONFIG_SHELL) $(systbl) --abis $(abis),$* \
> +		   --common-tbl $(syscalltbl_common) $< $@

[Severity: High]
Does pulling in the common syscall table break OABI compatibility for
32-bit ARM?

The common table populates the compat column with compat_sys_* functions
intended for CONFIG_COMPAT, for example:

scripts/syscall_common.tbl:
    413  32  pselect6_time64  sys_pselect6  compat_sys_pselect6_time64

However, ARM OABI redefines __SYSCALL_WITH_COMPAT to use the compat column
specifically for its own OABI wrappers, not for 64-bit-on-32-bit compat
wrappers:

arch/arm/kernel/entry-common.S:sys_oabi_call_table() {
    #undef __SYSCALL_WITH_COMPAT
    #define __SYSCALL_WITH_COMPAT(nr, native, compat) __SYSCALL(nr, compat)
}

This clash causes build failures like "undefined reference to
compat_sys_pselect6_time64" during linking when CONFIG_OABI_COMPAT is enabled.
For syscalls with weak stubs in kernel/sys_ni.c (like io_pgetevents_time64),
the build succeeds but OABI binaries will silently receive -ENOSYS at runtime.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=4