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manual: describe syscall numbers not supported via syscall() 

The syscall() function allows to make system calls directly, however,
in the case of system calls that affect internal state of process or
thread, the caller would have to take care of extensive setup necessary
for the internals of Glibc to work correctly in the child threads. This
may make using syscall() with these syscall numbers impractical and
prone to undefined behaviour.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
This commit is contained in:
Yury Khrustalev 2025-06-20 13:37:34 +01:00
parent ed5b1fad62
commit b96031cb56
1 changed files with 6 additions and 1 deletions
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7
manual/startup.texi
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@ -737,6 +737,12 @@ anyway.
@code{syscall} does not provide cancellation logic, even if the system
call you're calling is listed as cancellable above.
Using @code{syscall} with system calls that affect the internal state of
process of thread will likely result in undefined behavior. For this reason,
at least the following system call numbers are not supported when invoked via
@code{syscall}: @code{SYS_clone}, @code{SYS_clone2}, @code{SYS_clone3},
@code{SYS_rt_sigreturn}, @code{SYS_sigreturn}, @code{SYS_vfork}.
@code{syscall} is declared in @file{unistd.h}.
@deftypefun {long int} syscall (long int @var{sysno}, @dots{})
@ -804,7 +810,6 @@ if (rc == -1)
@end deftypefun
@node Program Termination
@section Program Termination
@cindex program termination