From 1f2a3fee025f763f3e7c6f6147069b8a6008018e Mon Sep 17 00:00:00 2001 From: Joel Brobecker Date: Tue, 25 Oct 2011 12:17:08 -0400 Subject: [PATCH] [ia64-linux] Allow libunwind to fetch register 0 On ia64-linux, GDB sometimes prints the following error when trying to switch to a different task: (gdb) task 3 Register 0 is not available This is a random failure that sometimes happens, sometimes does not. The error comes from the fact that the libunwind library is requesting the value of register 0 (zero): This eventually leads us to ia64-linux-nat.c:ia64_linux_fetch_register. This function relies on ia64_cannot_fetch_register to determine whether or not we have access to the register's value. The ptrace interface does not provide the r0 value, and so we end up telling the regcache that this register's value is not available. And yet, for r0, we do not need to ask ptrace for its value, since it is always zero. So, the fix was to add a special rule for supplying a nul value when regnum == 0. gdb/ChangeLog: * ia64-linux-nat.c (ia64_linux_fetch_register): Add special handling for r0. --- gdb/ia64-linux-nat.c | 10 ++++++++++ 1 files changed, 10 insertions(+), 0 deletions(-) diff --git a/gdb/ia64-linux-nat.c b/gdb/ia64-linux-nat.c index 19b827f..60b873b 100644 --- a/gdb/ia64-linux-nat.c +++ b/gdb/ia64-linux-nat.c @@ -680,6 +680,16 @@ ia64_linux_fetch_register (struct regcache *regcache, int regnum) PTRACE_TYPE_RET *buf; int pid, i; + /* r0 cannot be fetched but is always zero. */ + if (regnum == IA64_GR0_REGNUM) + { + const gdb_byte zero[8] = { 0 }; + + gdb_assert (sizeof (zero) == register_size (gdbarch, regnum)); + regcache_raw_supply (regcache, regnum, zero); + return; + } + if (ia64_cannot_fetch_register (gdbarch, regnum)) { regcache_raw_supply (regcache, regnum, NULL); -- 1.7.1