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sh: make sigcontext definition consistent across fpu/nofpu models

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Up until now, the SH version of the sigcontext structure, and thus
mcontext_t/ucontext_t, varied depending on the cpu model the kernel
was built to run on. SH-4 (including SH-4A) and SH-2A used the form
with space for FPU registers, and everything else used a form that
omitted them.

From a userspace perspective, however, the structure layout must be
fixed for a given ABI. Traditionally glibc and uClibc used the form
with space for FPU registers only when __SH4__ (which implies FPU;
__SH4_NOFPU__ is the predefined macro for SH-4 but with no-FPU ABI)
was defined. As a result:

- SH-4 no-FPU programs never matched kernel sigcontext.

- SH-3 programs did not match kernel sigcontext if run on SH-4,
  despite an apparent intent that they be compatible.

- SH-2 and SH-2A programs (using uClibc) did not match kernel
  sigcontext if run on SH-2A.

The mismatch might seem inconsequential because it occurs at the end
of the sigcontext structure, but sigcontext is embedded as uc_mcontext
in ucontext_t, where it is followed by uc_sigmask, an important member
for signal handlers to have access to. In particular, access to
uc_sigmask is necessary for a correct implementation of thread
cancellation.

It would be possible to retain support for both sigcontext ABIs via a
personality mechanism, but since many configurations were already
broken and nobody noticed, and since there are very few if any users
of legacy no-FPU models anymore, I have opted to just remove the
variation and always include space for the FPU registers in
sigcontext. This was proposed and discussed on a thread "SH sigcontext
ABI is broken" cross-posted to linux-sh, libc-alpha, and musl libc
lists in June 2015, and no objections were raised.

Signed-off-by: Rich Felker <dalias@libc.org>
This commit is contained in:
Rich Felker 2016-04-01 20:10:19 +00:00
parent 190fe191cf
commit bbe6c77857
1 changed files with 0 additions and 3 deletions
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3
arch/sh/include/uapi/asm/sigcontext.h
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@ -25,8 +25,6 @@ struct sigcontext {
unsigned long sc_mach;
unsigned long sc_macl;
#if defined(__SH4__) || defined(CONFIG_CPU_SH4) || \
defined(__SH2A__) || defined(CONFIG_CPU_SH2A)
/* FPU registers */
unsigned long sc_fpregs[16];
unsigned long sc_xfpregs[16];
@ -34,7 +32,6 @@ struct sigcontext {
unsigned int sc_fpul;
unsigned int sc_ownedfp;
#endif
#endif
};
#endif /* __ASM_SH_SIGCONTEXT_H */