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From: "Alex Bennée" <alex.bennee@linaro.org>
To: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Cc: "Rowan Hart" <rowanbhart@gmail.com>,
	qemu-devel@nongnu.org,
	"Richard Henderson" <richard.henderson@linaro.org>,
	"Mahmoud Mandour" <ma.mandourr@gmail.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Marcel Apfelbaum" <marcel.apfelbaum@gmail.com>,
	"Yanan Wang" <wangyanan55@huawei.com>,
	"Alexandre Iooss" <erdnaxe@crans.org>,
	"Eduardo Habkost" <eduardo@habkost.net>,
	"Zhao Liu" <zhao1.liu@intel.com>,
	"Philippe Mathieu-Daudé" <philmd@linaro.org>
Subject: Re: [PATCH v14 0/8] Add additional plugin API functions to read and write memory and registers
Date: Fri, 27 Jun 2025 19:26:30 +0100	[thread overview]
Message-ID: <871pr5yrah.fsf@draig.linaro.org> (raw)
In-Reply-To: <5f50e512-818f-465a-970e-04873ee2dc77@linaro.org> (Pierrick Bouvier's message of "Fri, 27 Jun 2025 09:18:00 -0700")

Pierrick Bouvier <pierrick.bouvier@linaro.org> writes:

> On 6/27/25 2:17 AM, Alex Bennée wrote:
>> Pierrick Bouvier <pierrick.bouvier@linaro.org> writes:
>> 
>>> On 6/26/25 9:37 AM, Alex Bennée wrote:
>>>> Alex Bennée <alex.bennee@linaro.org> writes:
>>>>
>>>>> Rowan Hart <rowanbhart@gmail.com> writes:
>>>>>
>>>>>> This patch series adds several new API functions focused on enabling use
>>>>>> cases around reading and writing guest memory from QEMU plugins. To support
>>>>>> these new APIs, some utility functionality around retrieving information about
>>>>>> address spaces is added as well.
>>>>>
>>>>> Queued to plugins/next, thanks.
>>>> So this fails a number of the CI tests, mostly due to 32 bit issues:
>>>>     https://gitlab.com/stsquad/qemu/-/pipelines/1890883927/failures
>>>> The tci failure is easy enough:
>>>> --8<---------------cut here---------------start------------->8---
>>>> modified   tests/tcg/x86_64/Makefile.softmmu-target
>>>> @@ -34,9 +34,11 @@ memory: CFLAGS+=-DCHECK_UNALIGNED=1
>>>>    # Running
>>>>    QEMU_OPTS+=-device isa-debugcon,chardev=output -device isa-debug-exit,iobase=0xf4,iosize=0x4 -kernel
>>>>    +ifeq ($(CONFIG_PLUGIN),y)
>>>>    run-plugin-patch-target-with-libpatch.so:		\
>>>>    	PLUGIN_ARGS=$(COMMA)target=ffc0$(COMMA)patch=9090$(COMMA)use_hwaddr=true
>>>>    run-plugin-patch-target-with-libpatch.so:		\
>>>>    	CHECK_PLUGIN_OUTPUT_COMMAND=$(X64_SYSTEM_SRC)/validate-patch.py $@.out
>>>>    run-plugin-patch-target-with-libpatch.so: patch-target libpatch.so
>>>>    EXTRA_RUNS+=run-plugin-patch-target-with-libpatch.so
>>>> +endif
>>>> --8<---------------cut here---------------end--------------->8---
>>>> The other problem is trying to stuff a uint64_t into a void * on 32
>>>> bit.
>>>> We did disable plugins for 32 bit but then reverted because we were able
>>>> to fixup the cases:
>>>>    cf2a78cbbb (deprecation: don't enable TCG plugins by default on 32
>>>> bit hosts)
>>>>    db7a06ade1 (configure: reenable plugins by default for 32-bit hosts)
>>>> So I don't what is easier:
>>>>    - re-deprecate for 32 bit systems
>>>>    - only build libpatch on 64 bit systems
>>>>    - fix libpatch to handle being built on 32 bit systems
>>>>
>>>
>>> More context:
>>> ../tests/tcg/plugins/patch.c: In function ‘patch_hwaddr’:
>>> ../tests/tcg/plugins/patch.c:50:21: error: cast from pointer to
>>> integer of different size [-Werror=pointer-to-int-cast]
>>>     50 |     uint64_t addr = (uint64_t)userdata;
>>>        |                     ^
>>> ../tests/tcg/plugins/patch.c: In function ‘patch_vaddr’:
>>> ../tests/tcg/plugins/patch.c:93:21: error: cast from pointer to
>>> integer of different size [-Werror=pointer-to-int-cast]
>>>     93 |     uint64_t addr = (uint64_t)userdata;
>>>        |                     ^
>>> ../tests/tcg/plugins/patch.c: In function ‘vcpu_tb_trans_cb’:
>>> ../tests/tcg/plugins/patch.c:159:54: error: cast to pointer from
>>> integer of different size [-Werror=int-to-pointer-cast]
>>>    159 |                                                      (void *)addr);
>>>        |                                                      ^
>>> ../tests/tcg/plugins/patch.c:163:54: error: cast to pointer from
>>> integer of different size [-Werror=int-to-pointer-cast]
>>>    163 |                                                      (void *)addr);
>>>        |
>>>
>>> Since we disabled 64 bit targets on 32 bit hosts, and that data passed
>>> by pointers concern addresses, it should be safe to cast values to
>>> (uintptr_t) instead of (uint64_t).
>> Something like this?
>> --8<---------------cut here---------------start------------->8---
>> modified   tests/tcg/plugins/patch.c
>> @@ -47,10 +47,10 @@ static GByteArray *str_to_bytes(const char *str)
>>     static void patch_hwaddr(unsigned int vcpu_index, void
>> *userdata)
>>   {
>> -    uint64_t addr = (uint64_t)userdata;
>> +    uintptr_t addr = (uintptr_t) userdata;
>>       g_autoptr(GString) str = g_string_new(NULL);
>>       g_string_printf(str, "patching: @0x%"
>> -                    PRIx64 "\n",
>> +                    PRIxPTR "\n",
>>                       addr);
>>       qemu_plugin_outs(str->str);
>>   @@ -90,7 +90,7 @@ static void patch_hwaddr(unsigned int
>> vcpu_index, void *userdata)
>>     static void patch_vaddr(unsigned int vcpu_index, void *userdata)
>>   {
>> -    uint64_t addr = (uint64_t)userdata;
>> +    uintptr_t addr = (uintptr_t) userdata;
>>       uint64_t hwaddr = 0;
>>       if (!qemu_plugin_translate_vaddr(addr, &hwaddr)) {
>>           qemu_plugin_outs("Failed to translate vaddr\n");
>> @@ -98,7 +98,7 @@ static void patch_vaddr(unsigned int vcpu_index, void *userdata)
>>       }
>>       g_autoptr(GString) str = g_string_new(NULL);
>>       g_string_printf(str, "patching: @0x%"
>> -                    PRIx64 " hw: @0x%" PRIx64 "\n",
>> +                    PRIxPTR " hw: @0x%" PRIx64 "\n",
>>                       addr, hwaddr);
>>       qemu_plugin_outs(str->str);
>>   @@ -132,19 +132,29 @@ static void patch_vaddr(unsigned int
>> vcpu_index, void *userdata)
>>    */
>>   static void vcpu_tb_trans_cb(qemu_plugin_id_t id, struct qemu_plugin_tb *tb)
>>   {
>> -    uint64_t addr = 0;
>>       g_autoptr(GByteArray) insn_data = g_byte_array_new();
>> +    uintptr_t addr = 0;
>> +
>>       for (size_t i = 0; i < qemu_plugin_tb_n_insns(tb); i++) {
>>           struct qemu_plugin_insn *insn = qemu_plugin_tb_get_insn(tb, i);
>> +        uint64_t vaddr = qemu_plugin_insn_vaddr(insn);
>>             if (use_hwaddr) {
>> -            uint64_t vaddr = qemu_plugin_insn_vaddr(insn);
>> -            if (!qemu_plugin_translate_vaddr(vaddr, &addr)) {
>> +            uint64_t hwaddr = 0;
>> +            if (!qemu_plugin_translate_vaddr(vaddr, &hwaddr)) {
>>                   qemu_plugin_outs("Failed to translate vaddr\n");
>>                   continue;
>>               }
>> +            /*
>> +             * As we cannot emulate 64 bit systems on 32 bit hosts we
>> +             * should never see the top bits set, hence we can safely
>> +             * cast to uintptr_t.
>> +             */
>> +            g_assert(!(hwaddr & ~UINTPTR_MAX));
>
> We would have so many other problems before plugins if this hypothesis
> was not true (all the usage of vaddr type in the codebase would be
> broken). So the assert will not detect anything we are not aware about
> already.
>
> If we want to mention this assumption for plugins users, the plugins
> documentation is probably a better place than one random plugin.

Well we could change the API function signature to return uintptr_t?

>
>> +            addr = (uintptr_t) hwaddr;
>>           } else {
>> -            addr = qemu_plugin_insn_vaddr(insn);
>> +            g_assert(!(vaddr & ~UINTPTR_MAX));
>> +            addr = (uintptr_t) vaddr;
>>           }
>>             g_byte_array_set_size(insn_data,
>> qemu_plugin_insn_size(insn));
>> @@ -156,11 +166,11 @@ static void vcpu_tb_trans_cb(qemu_plugin_id_t id, struct qemu_plugin_tb *tb)
>>               if (use_hwaddr) {
>>                   qemu_plugin_register_vcpu_tb_exec_cb(tb, patch_hwaddr,
>>                                                        QEMU_PLUGIN_CB_NO_REGS,
>> -                                                     (void *)addr);
>> +                                                     (void *) addr);
>>               } else {
>>                   qemu_plugin_register_vcpu_tb_exec_cb(tb, patch_vaddr,
>>                                                        QEMU_PLUGIN_CB_NO_REGS,
>> -                                                     (void *)addr);
>> +                                                     (void *) addr);
>>               }
>>           }
>>       }
>> --8<---------------cut here---------------end--------------->8---
>> 
>>>
>>> Pierrick
>> 
>
> For the rest, it looks good to me.
>
> Thanks,
> Pierrick

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro


  reply	other threads:[~2025-06-27 18:27 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-06-24 17:53 [PATCH v14 0/8] Add additional plugin API functions to read and write memory and registers Rowan Hart
2025-06-24 17:53 ` [PATCH v14 1/8] gdbstub: Expose gdb_write_register function to consumers of gdbstub Rowan Hart
2025-06-24 17:53 ` [PATCH v14 2/8] plugins: Add register write API Rowan Hart
2025-06-24 17:53 ` [PATCH v14 3/8] plugins: Add enforcement of QEMU_PLUGIN_CB flags in register R/W callbacks Rowan Hart
2025-06-24 17:53 ` [PATCH v14 4/8] plugins: Add memory virtual address write API Rowan Hart
2025-06-24 17:53 ` [PATCH v14 5/8] plugins: Add memory hardware address read/write API Rowan Hart
2025-06-24 17:53 ` [PATCH v14 6/8] tests/tcg: Remove copy-pasted notes and from i386 and add x86_64 system tests to tests Rowan Hart
2025-06-24 17:53 ` [PATCH v14 7/8] plugins: Add patcher plugin and test Rowan Hart
2025-06-24 17:53 ` [PATCH v14 8/8] plugins: Update plugin version and add notes Rowan Hart
2025-06-25 14:51 ` [PATCH v14 0/8] Add additional plugin API functions to read and write memory and registers Alex Bennée
2025-06-26 16:37   ` Alex Bennée
2025-06-26 18:23     ` Pierrick Bouvier
2025-06-27  9:17       ` Alex Bennée
2025-06-27 16:18         ` Pierrick Bouvier
2025-06-27 18:26           ` Alex Bennée [this message]
2025-06-27 18:40             ` Pierrick Bouvier

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