| Message ID | 20240328224850.2785280-2-gustavo.romero@linaro.org |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Add another way to check for MTE-tagged addresses on remote targets | expand |
Gustavo Romero <gustavo.romero@linaro.org> writes: > This commit removes aarch64_linux_tagged_address_p from > aarch64_linux_get_memtag. aarch64_linux_tagged_address_p checks if an > address is tagged (MTE) or not. > > The check is redundant because aarch64_linux_get_memtag is always called > from the upper layers (i.e. from printcmd.c via gdbarch hook > gdbarch_get_memtag) after either gdbarch_tagged_address_p (that already > points to aarch64_linux_tagged_address_p) has been called or > after should_validate_memtags (that calls gdbarch_tagged_address_p at > the end) has been called, so the address is already checked. Hence: > > a) in print_command_1, aarch64_linux_get_memtag (via gdbarch_get_memtag > hook) is called but only after should_validate_memtags, which calls > gdbarch_tagged_address_p; > > b) in do_examine, aarch64_linux_get_memtag is also called only after > gdbarch_tagged_address_p is directly called; > > c) in memory_tag_check_command, gdbarch_get_memtag is called -- tags > matching or not -- after the initial check via direct call to > gdbarch_tagged_address_p; > > d) in memory_tag_print_tag_command, address is checked directly via > gdbarch_tagged_address_p before gdbarch_get_memtag is called. In cases c) and d), gdbarch_get_memtag gets called even if gdbarch_tagged_address_p returns false, so won't this commit change the behaviour of those functions in that case? I don't know enough about MTE to be sure. -- Thiago
Thiago Jung Bauermann <thiago.bauermann@linaro.org> writes: > Gustavo Romero <gustavo.romero@linaro.org> writes: > >> This commit removes aarch64_linux_tagged_address_p from >> aarch64_linux_get_memtag. aarch64_linux_tagged_address_p checks if an >> address is tagged (MTE) or not. >> >> The check is redundant because aarch64_linux_get_memtag is always called >> from the upper layers (i.e. from printcmd.c via gdbarch hook >> gdbarch_get_memtag) after either gdbarch_tagged_address_p (that already >> points to aarch64_linux_tagged_address_p) has been called or >> after should_validate_memtags (that calls gdbarch_tagged_address_p at >> the end) has been called, so the address is already checked. Hence: >> >> a) in print_command_1, aarch64_linux_get_memtag (via gdbarch_get_memtag >> hook) is called but only after should_validate_memtags, which calls >> gdbarch_tagged_address_p; >> >> b) in do_examine, aarch64_linux_get_memtag is also called only after >> gdbarch_tagged_address_p is directly called; >> >> c) in memory_tag_check_command, gdbarch_get_memtag is called -- tags >> matching or not -- after the initial check via direct call to >> gdbarch_tagged_address_p; >> >> d) in memory_tag_print_tag_command, address is checked directly via >> gdbarch_tagged_address_p before gdbarch_get_memtag is called. > > In cases c) and d), gdbarch_get_memtag gets called even if > gdbarch_tagged_address_p returns false, so won't this commit change the > behaviour of those functions in that case? I don't know enough about MTE > to be sure. I just realised that in cases c) and d) an error will be thrown by show_addr_not_tagged if gdbarch_tagged_address_p returns false, so gdbarch_get_memtag doesn't get called in that case and my concern isn't valid. Sorry about that. Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org> -- Thiago
Hi Thiago, On 3/29/24 9:55 PM, Thiago Jung Bauermann wrote: > Thiago Jung Bauermann <thiago.bauermann@linaro.org> writes: > >> Gustavo Romero <gustavo.romero@linaro.org> writes: >> >>> This commit removes aarch64_linux_tagged_address_p from >>> aarch64_linux_get_memtag. aarch64_linux_tagged_address_p checks if an >>> address is tagged (MTE) or not. >>> >>> The check is redundant because aarch64_linux_get_memtag is always called >>> from the upper layers (i.e. from printcmd.c via gdbarch hook >>> gdbarch_get_memtag) after either gdbarch_tagged_address_p (that already >>> points to aarch64_linux_tagged_address_p) has been called or >>> after should_validate_memtags (that calls gdbarch_tagged_address_p at >>> the end) has been called, so the address is already checked. Hence: >>> >>> a) in print_command_1, aarch64_linux_get_memtag (via gdbarch_get_memtag >>> hook) is called but only after should_validate_memtags, which calls >>> gdbarch_tagged_address_p; >>> >>> b) in do_examine, aarch64_linux_get_memtag is also called only after >>> gdbarch_tagged_address_p is directly called; >>> >>> c) in memory_tag_check_command, gdbarch_get_memtag is called -- tags >>> matching or not -- after the initial check via direct call to >>> gdbarch_tagged_address_p; >>> >>> d) in memory_tag_print_tag_command, address is checked directly via >>> gdbarch_tagged_address_p before gdbarch_get_memtag is called. >> >> In cases c) and d), gdbarch_get_memtag gets called even if >> gdbarch_tagged_address_p returns false, so won't this commit change the >> behaviour of those functions in that case? I don't know enough about MTE >> to be sure. > > I just realised that in cases c) and d) an error will be thrown by > show_addr_not_tagged if gdbarch_tagged_address_p returns false, so > gdbarch_get_memtag doesn't get called in that case and my concern isn't > valid. Sorry about that. Yeah. No worries, I also missed that show_addr_not_tagged throws an error the first time I read this part, it looked like just printing function :) > Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org> Thanks for the review. Cheers, Gustavo
diff --git a/gdb/aarch64-linux-tdep.c b/gdb/aarch64-linux-tdep.c index 0b9784f38e4..50055ac3f48 100644 --- a/gdb/aarch64-linux-tdep.c +++ b/gdb/aarch64-linux-tdep.c @@ -2575,10 +2575,6 @@ aarch64_linux_get_memtag (struct gdbarch *gdbarch, struct value *address, tag = aarch64_mte_get_ltag (addr); else { - /* Make sure we are dealing with a tagged address to begin with. */ - if (!aarch64_linux_tagged_address_p (gdbarch, address)) - return nullptr; - /* Remove the top byte. */ addr = gdbarch_remove_non_address_bits (gdbarch, addr); std::optional<CORE_ADDR> atag = aarch64_mte_get_atag (addr);
This commit removes aarch64_linux_tagged_address_p from aarch64_linux_get_memtag. aarch64_linux_tagged_address_p checks if an address is tagged (MTE) or not. The check is redundant because aarch64_linux_get_memtag is always called from the upper layers (i.e. from printcmd.c via gdbarch hook gdbarch_get_memtag) after either gdbarch_tagged_address_p (that already points to aarch64_linux_tagged_address_p) has been called or after should_validate_memtags (that calls gdbarch_tagged_address_p at the end) has been called, so the address is already checked. Hence: a) in print_command_1, aarch64_linux_get_memtag (via gdbarch_get_memtag hook) is called but only after should_validate_memtags, which calls gdbarch_tagged_address_p; b) in do_examine, aarch64_linux_get_memtag is also called only after gdbarch_tagged_address_p is directly called; c) in memory_tag_check_command, gdbarch_get_memtag is called -- tags matching or not -- after the initial check via direct call to gdbarch_tagged_address_p; d) in memory_tag_print_tag_command, address is checked directly via gdbarch_tagged_address_p before gdbarch_get_memtag is called. Also, because after this change the address checking only happens at the upper layer it now allows the address checking to be specialized easily per target, via a target hook. Signed-off-by: Gustavo Romero <gustavo.romero@linaro.org> --- gdb/aarch64-linux-tdep.c | 4 ---- 1 file changed, 4 deletions(-)