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[committed] MIPS/Linux: Disable n32 USR `ptrace' accesses to 64-bit registers
- From: "Maciej W. Rozycki" <macro at mips dot com>
- To: <gdb-patches at sourceware dot org>
- Date: Tue, 22 May 2018 01:54:02 +0100
- Subject: [committed] MIPS/Linux: Disable n32 USR `ptrace' accesses to 64-bit registers
On the MIPS target DSP ASE registers can only be accessed with the
PTRACE_PEEKUSR and PTRACE_POKEUSR `ptrace' requests. With the n32 ABI
these requests only pass 32-bit data quantities, which are narrower than
the width of DSP accumulator registers, which are 64-bit.
Generic code is prepared to transfer registers wider than the `ptrace'
data type by offsetting into the USR address space, by the data width
transferred. That however does not work with the MIPS target, because
of how the API has been defined, where USR register addresses are
actually indices rather than offsets. Consequently given address `a'
using `a + 4' accesses the fourth next register rather than the upper
half of the original register.
With native debugging this causes clobbered register contents, as well
as access failures as locations beyond the available USR space are
addressed:
(gdb) info registers
zero at v0 v1
R0 0000000000000000 0000000000000001 0000000000000001 0000000000000000
a0 a1 a2 a3
R4 0000000010019158 0000000000000000 0000000000000011 0000000010019160
a4 a5 a6 a7
R8 0000000010019160 fffffffffff00000 fffffffffffffff8 0000000000000000
t0 t1 t2 t3
R12 0000000010019150 0000000000000001 0000000000000001 000000000000000f
s0 s1 s2 s3
R16 0000000077ee6f20 0000000010007bb0 0000000000000000 0000000000000000
s4 s5 s6 s7
R20 000000000052e668 000000000052f008 0000000000000000 0000000000000000
t8 t9 k0 k1
R24 0000000000000001 0000000010019010 0000000000000000 0000000000000000
gp sp s8 ra
R28 0000000010020280 000000007fff4c10 000000007fff4c10 0000000010004f48
status lo hi badvaddr
0000000000109cf3 0000000000943efe 000000000000000e 000000001001900c
cause pc
0000000000800024 0000000010004f48
fcsr fir hi1 lo1
0e800000 00f30000 0000000004040404 0101010105050505
hi2 lo2 hi3 lo3
0202020255aa33cc Couldn't read register (#75): Input/output error.
(gdb)
With `gdbserver' this makes debugging impossible due to a fatal failure:
(gdb) target remote :2346
Remote debugging using :2346
Reading symbols from .../sysroot/mips-r2-hard/lib32/ld.so.1...done.
0x77fc3d50 in __start () from .../sysroot/mips-r2-hard/lib32/ld.so.1
(gdb) continue
Continuing.
warning: Remote failure reply: E01
Remote communication error. Target disconnected.: Connection reset by peer.
(gdb)
Correct the problem by marking any register in the MIPS backend whose
width exceeds the width of the `ptrace' data type unavailable for the
purpose of PTRACE_PEEKUSR and PTRACE_POKEUSR requests:
(gdb) info registers
zero at v0 v1
R0 0000000000000000 0000000000000001 0000000000000001 0000000000000000
a0 a1 a2 a3
R4 0000000010019158 0000000000000000 0000000000000011 0000000010019160
a4 a5 a6 a7
R8 0000000010019160 fffffffffff00000 fffffffffffffff8 0000000000000000
t0 t1 t2 t3
R12 0000000010019150 0000000000000001 0000000000000001 000000000000000f
s0 s1 s2 s3
R16 0000000077ee6f20 0000000010007bb0 0000000000000000 0000000000000000
s4 s5 s6 s7
R20 000000000052e5c8 000000000052f008 0000000000000000 0000000000000000
t8 t9 k0 k1
R24 0000000000000001 0000000010019010 0000000000000000 0000000000000000
gp sp s8 ra
R28 0000000010020280 000000007fff4be0 000000007fff4be0 0000000010004f48
status lo hi badvaddr
0000000000109cf3 0000000000943efe 000000000000000e 000000001001900c
cause pc
0000000000800024 0000000010004f48
fcsr fir hi1 lo1
0e800000 00f30000 <unavailable> <unavailable>
hi2 lo2 hi3 lo3
<unavailable> <unavailable> <unavailable> <unavailable>
dspctl restart
55aa33cc 0000000000000000
(gdb)
as there is no way to access full contents of these registers with the
limited API available anyway.
This obviously does not affect general-purpose registers (which use the
PTRACE_GETREGS and PTRACE_SETREGS requests for access) or floating-point
general registers (which use PTRACE_GETFPREGS and PTRACE_SETFPREGS).
And $dspctl, being 32-bit, remains accessible too, which is important
for BPOSGE32 branch decoding in single-stepping.
For DSP accumulator access with the n32 ABI a new `ptrace' API is required
on the kernel side.
gdb/
* mips-linux-nat.c (mips64_linux_register_addr): Return -1 if
the width of the requested register exceeds the width of the
`ptrace' data type.
gdb/gdbserver/
* linux-mips-low.c (mips_cannot_fetch_register): Return 1 if the
width of the requested register exceeds the width of the
`ptrace' data type.
(mips_cannot_store_register): Likewise.
---
Hi,
A kernel `ptrace' API update has been posted:
<https://patchwork.kernel.org/patch/10402171/>
<https://patchwork.linux-mips.org/patch/19330/>
Once that has been accepted the GDB side can be updated accordingly, and
DSP register state handling also added to core file support.
No native or native-gdbserver regressions across the three MIPS ABIs.
Committed.
Maciej
---
gdb/gdbserver/linux-mips-low.c | 8 ++++++++
gdb/mips-linux-nat.c | 5 +++++
2 files changed, 13 insertions(+)
gdb-mips-n32-dsp-disable.diff
Index: binutils/gdb/gdbserver/linux-mips-low.c
===================================================================
--- binutils.orig/gdb/gdbserver/linux-mips-low.c 2018-02-23 14:14:24.000000000 +0000
+++ binutils/gdb/gdbserver/linux-mips-low.c 2018-05-18 02:39:22.987236110 +0100
@@ -211,6 +211,10 @@ mips_cannot_fetch_register (int regno)
tdesc = current_process ()->tdesc;
+ /* On n32 we can't access 64-bit registers via PTRACE_PEEKUSR. */
+ if (register_size (tdesc, regno) > sizeof (PTRACE_XFER_TYPE))
+ return 1;
+
if (find_regno (tdesc, "r0") == regno)
return 1;
@@ -227,6 +231,10 @@ mips_cannot_store_register (int regno)
tdesc = current_process ()->tdesc;
+ /* On n32 we can't access 64-bit registers via PTRACE_POKEUSR. */
+ if (register_size (tdesc, regno) > sizeof (PTRACE_XFER_TYPE))
+ return 1;
+
if (find_regno (tdesc, "r0") == regno)
return 1;
Index: binutils/gdb/mips-linux-nat.c
===================================================================
--- binutils.orig/gdb/mips-linux-nat.c 2018-05-17 17:25:26.000000000 +0100
+++ binutils/gdb/mips-linux-nat.c 2018-05-18 02:54:39.440985218 +0100
@@ -145,6 +145,11 @@ mips64_linux_register_addr (struct gdbar
if (regno < 0 || regno >= gdbarch_num_regs (gdbarch))
error (_("Bogon register number %d."), regno);
+ /* On n32 we can't access 64-bit registers via PTRACE_PEEKUSR
+ or PTRACE_POKEUSR. */
+ if (register_size (gdbarch, regno) > sizeof (PTRACE_TYPE_RET))
+ return (CORE_ADDR) -1;
+
if (regno > MIPS_ZERO_REGNUM && regno < MIPS_ZERO_REGNUM + 32)
regaddr = regno;
else if ((regno >= mips_regnum (gdbarch)->fp0)