Re: [PATCH 1/4] glibc: Perform rseq(2) registration at C startup and thread creation (v7)

On Mon, 25 Mar 2019 11:54:32 -0400 (EDT)
Mathieu Desnoyers [off-list ref] wrote:

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+++ b/sysdeps/unix/sysv/linux/s390/bits/rseq.h  

[...]

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+
+/* Signature required before each abort handler code.  */
+#define RSEQ_SIG 0x53053053  

Why not a s390 specific value here?  

s390 also has the abort handler in a __rseq_failure section:

#define RSEQ_ASM_DEFINE_ABORT(label, teardown, abort_label)             \
                ".pushsection __rseq_failure, \"ax\"\n\t"               \
                ".long " __rseq_str(RSEQ_SIG) "\n\t"                    \
                __rseq_str(label) ":\n\t"                               \
                teardown                                                \
                "j %l[" __rseq_str(abort_label) "]\n\t"                 \
                ".popsection\n\t"

Same question applies as powerpc: since disassemblers will try to decode
that instruction, would it be better to define it as a valid one ?

[...]

A 4-byte sequence starting with 0x53 is decoded as a "diebr" instruction.
And please replace that "j %l[...]" with a "jg %l[...]", the branch target
range of the "j" instruction is 64K, not enough for the general case.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.