[gdb/tdep] Fix gdb.base/watchpoint-running.exp on {arm,ppc64le}-linux
When running test-case gdb.base/watchpoint-running on ppc64le-linux (and similar on arm-linux), we get: ... (gdb) watch global_var^M warning: Error when detecting the debug register interface. \ Debug registers will be unavailable.^M Watchpoint 2: global_var^M (gdb) FAIL: $exp: all-stop: hardware: watch global_var FAIL: $exp: all-stop: hardware: watchpoint hit (timeout) ... The problem is that ppc_linux_dreg_interface::detect fails to detect the hardware watchpoint interface, because the calls to ptrace return with errno set to ESRCH. This is a feature of ptrace: if a call is done while the tracee is not ptrace-stopped, it returns ESRCH. Indeed, in the test-case "watch global_var" is executed while the inferior is running, and that triggers the first call to ppc_linux_dreg_interface::detect. And because the detection failure is cached, subsequent attempts at setting hardware watchpoints will also fail, even if the tracee is ptrace-stopped. The way to fix this is to make sure that ppc_linux_dreg_interface::detect is called when we know that the thread is ptrace-stopped, which in the current setup is best addressed by using target-specific post_attach and post_startup_inferior overrides. However, as we can see in aarch64_linux_nat_target, that causes code duplication. Fix this by: - defining a new target hook low_init_process, called from linux_init_ptrace_procfs, which is called from both linux_nat_target::post_attach and linux_nat_target::post_startup_inferior, - adding implementations for ppc_linux_nat_target and arm_linux_nat_target that detect the hardware watchpoint interface, - replacing the aarch64_linux_nat_target implementations of post_attach and post_startup_inferior with a low_init_process implementation. Tested on ppc64le-linux, arm-linux, aarch64-linux and x86_64-linux. Co-Authored-By:Tom de Vries <tdevries@suse.de> Approved-By:
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