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[committed] MIPS/Linux/native: Supply $zero for the !PTRACE_GETREGS case
- From: "Maciej W. Rozycki" <macro at mips dot com>
- To: <gdb-patches at sourceware dot org>
- Date: Tue, 15 May 2018 16:27:07 +0100
- Subject: [committed] MIPS/Linux/native: Supply $zero for the !PTRACE_GETREGS case
With native MIPS/Linux targets the $zero register is inaccessible, with
its supposed context slot provided by the OS occupied by the $restart
register. The PTRACE_GETREGS path takes care of it by artificially
supplying the hardwired contents of $zero in `mips_supply_gregset' or
`mips64_supply_gregset', as applicable, however the PTRACE_PEEKUSER
fallback does not, making the register unavailable, e.g.:
(gdb) info registers
zero at v0 v1 a0 a1 a2 a3
R0 <unavl> 00000001 00000001 d2f1a9fc 00000000 00000000 00417158 00417150
t0 t1 t2 t3 t4 t5 t6 t7
R8 00000004 00000000 fffffff8 00000000 00000000 00000000 00000001 00000007
s0 s1 s2 s3 s4 s5 s6 s7
R16 00000000 00405e30 00000000 00500000 00000000 0052ec08 00000000 00000000
t8 t9 k0 k1 gp sp s8 ra
R24 00000000 00417008 00000000 00000000 0041e220 7fff4ce0 7fff4ce0 00405d0c
status lo hi badvaddr cause pc
<unavl> 00441cf1 00000017 00417004 00800024 00405d10
fcsr fir restart
00800000 00f30000 00000000
(gdb)
or (under certain circumstances):
(gdb) stepi
Register 0 is not available
(gdb)
This is specifically because `mips_linux_register_addr' and
`mips64_linux_register_addr', both correctly return -1 for
MIPS_ZERO_REGNUM, and therefore `linux_nat_trad_target::fetch_registers'
faithfully marks this register as unavailable.
Supply this register artificially then in the PTRACE_PEEKUSER case as
well, correcting this issue.
gdb/
* mips-linux-nat.c (mips_linux_nat_target::fetch_registers):
Supply the MIPS_ZERO_REGNUM register.
---
gdb/mips-linux-nat.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
gdb-mips-linux-nat-zero-regno.diff
Index: binutils/gdb/mips-linux-nat.c
===================================================================
--- binutils.orig/gdb/mips-linux-nat.c 2018-05-12 06:56:28.000000000 +0100
+++ binutils/gdb/mips-linux-nat.c 2018-05-12 07:00:04.545527001 +0100
@@ -416,7 +416,13 @@ mips_linux_nat_target::fetch_registers (
/* If we know, or just found out, that PTRACE_GETREGS does not work, fall
back to PTRACE_PEEKUSER. */
if (!have_ptrace_regsets)
- linux_nat_trad_target::fetch_registers (regcache, regnum);
+ {
+ linux_nat_trad_target::fetch_registers (regcache, regnum);
+
+ /* Fill the inaccessible zero register with zero. */
+ if (regnum == MIPS_ZERO_REGNUM || regnum == -1)
+ regcache->raw_supply_zeroed (MIPS_ZERO_REGNUM);
+ }
}
/* Store REGNO (or all registers if REGNO == -1) to the target