On Wed, 2024-01-10 at 04:42 +1100, Richard Henderson wrote:
On 1/9/24 10:34, Ilya Leoshkevich wrote:
gdbserver ignores page protection by virtue of using
/proc/$pid/mem.
Teach qemu gdbstub to do this too. This will not work if /proc is
not
mounted; accept this limitation.
One alternative is to temporarily grant the missing PROT_* bit, but
this is inherently racy. Another alternative is self-debugging with
ptrace(POKE), which will break if QEMU itself is being debugged - a
much more severe limitation.
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
cpu-target.c | 55 ++++++++++++++++++++++++++++++++++++++---------
-----
1 file changed, 40 insertions(+), 15 deletions(-)
diff --git a/cpu-target.c b/cpu-target.c
index 5eecd7ea2d7..69e97f78980 100644
--- a/cpu-target.c
+++ b/cpu-target.c
@@ -406,6 +406,15 @@ int cpu_memory_rw_debug(CPUState *cpu, vaddr
addr,
vaddr l, page;
void * p;
uint8_t *buf = ptr;
+ int ret = -1;
+ int mem_fd;
+
+ /*
+ * Try ptrace first. If /proc is not mounted or if there is a
different
+ * problem, fall back to the manual page access. Note that,
unlike ptrace,
+ * it will not be able to ignore the protection bits.
+ */
+ mem_fd = open("/proc/self/mem", is_write ? O_WRONLY :
O_RDONLY);
Surely this is the unlikely fallback, and you don't need to open
unless the page is
otherwise inaccessible.
Ok, I can move this under (flags & PAGE_*) checks.
I see no handling for writes to pages that contain TranslationBlocks.
Sorry, I completely missed that. I'm currently experimenting with the
following:
/*
* If there is a TranslationBlock and we weren't bypassing
host
* page protection, the memcpy() above would SEGV, ultimately
* leading to page_unprotect(). So invalidate the translations
* manually. Both invalidation and pwrite() must be under
* mmap_lock() in order to prevent the creation of another
* TranslationBlock in between.
*/
mmap_lock();
tb_invalidate_phys_page(page);
written = pwrite(fd, buf, l, (off_t)g2h_untagged(addr));