----- On Apr 16, 2019, at 1:32 PM, Mathieu Desnoyers mathieu.desnoyers@xxxxxxxxxxxx wrote: [...] > diff --git a/sysdeps/unix/sysv/linux/aarch64/bits/rseq.h > b/sysdeps/unix/sysv/linux/aarch64/bits/rseq.h > new file mode 100644 > index 0000000000..b02471a89a > --- /dev/null > +++ b/sysdeps/unix/sysv/linux/aarch64/bits/rseq.h > @@ -0,0 +1,32 @@ > +/* Restartable Sequences Linux aarch64 architecture header. > + > + Copyright (C) 2019 Free Software Foundation, Inc. > + > + The GNU C Library is free software; you can redistribute it and/or > + modify it under the terms of the GNU Lesser General Public > + License as published by the Free Software Foundation; either > + version 2.1 of the License, or (at your option) any later version. > + > + The GNU C Library is distributed in the hope that it will be useful, > + but WITHOUT ANY WARRANTY; without even the implied warranty of > + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU > + Lesser General Public License for more details. > + > + You should have received a copy of the GNU Lesser General Public > + License along with the GNU C Library; if not, see > + <http://www.gnu.org/licenses/>. */ > + > +#ifndef _SYS_RSEQ_H > +# error "Never use <bits/rseq.h> directly; include <sys/rseq.h> instead." > +#endif > + > +/* RSEQ_SIG is a signature required before each abort handler code. > + > + It is a 32-bit value that maps to actual architecture code compiled > + into applications and libraries. It needs to be defined for each > + architecture. When choosing this value, it needs to be taken into > + account that generating invalid instructions may have ill effects on > + tools like objdump, and may also have impact on the CPU speculative > + execution efficiency in some cases. */ > + > +#define RSEQ_SIG 0xd428bc00 /* BRK #0x45E0. */ After further investigation, we should probably do the following to handle compiling with -mbig-endian on aarch64, which generates binaries with mixed code vs data endianness (little endian code, big endian data): #ifdef __ARM_BIG_ENDIAN #define RSEQ_SIG 0x00bc28d4 /* BRK #0x45E0. */ #else #define RSEQ_SIG 0xd428bc00 /* BRK #0x45E0. */ #endif Else mismatch between code endianness for the generated signatures and data endianness for the RSEQ_SIG parameter passed to the rseq registration will trigger application segmentation faults when the kernel try to abort rseq critical sections. For ARM32, the situation is a bit more complex. Only armv6+ generates mixed-endianness code vs data with -mbig-endian. Prior to armv6, the code and data endianness matches. Therefore, I plan to #ifdef the reversed endianness handling with: #if __ARM_ARCH >= 6 && __ARM_BIG_ENDIAN on arm32. Thoughts ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
