From 75d74ccace05f6166a45dbaa352abf753891d3be Mon Sep 17 00:00:00 2001 From: "Maciej W. Rozycki" Date: Tue, 22 May 2018 01:52:35 +0100 Subject: [PATCH] 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 hi2 lo2 hi3 lo3 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. --- gdb/ChangeLog | 6 ++++++ gdb/gdbserver/ChangeLog | 7 +++++++ gdb/gdbserver/linux-mips-low.c | 8 ++++++++ gdb/mips-linux-nat.c | 5 +++++ 4 files changed, 26 insertions(+) diff --git a/gdb/ChangeLog b/gdb/ChangeLog index 82e249f5639..8d425a72a0d 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,9 @@ +2018-05-22 Maciej W. Rozycki + + * 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. + 2018-05-21 Tom Tromey * printcmd.c (output_command): Remove. diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog index 3c554571fbe..c577b3d0562 100644 --- a/gdb/gdbserver/ChangeLog +++ b/gdb/gdbserver/ChangeLog @@ -1,3 +1,10 @@ +2018-05-22 Maciej W. Rozycki + + * 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. + 2018-05-21 Maciej W. Rozycki * linux-mips-low.c (mips_fetch_register): New function. Update diff --git a/gdb/gdbserver/linux-mips-low.c b/gdb/gdbserver/linux-mips-low.c index ff87dd77d37..7fae2e69844 100644 --- a/gdb/gdbserver/linux-mips-low.c +++ b/gdb/gdbserver/linux-mips-low.c @@ -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; diff --git a/gdb/mips-linux-nat.c b/gdb/mips-linux-nat.c index b1dbb798523..a9f0b790769 100644 --- a/gdb/mips-linux-nat.c +++ b/gdb/mips-linux-nat.c @@ -145,6 +145,11 @@ mips64_linux_register_addr (struct gdbarch *gdbarch, int regno, int store) 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) -- 2.30.2