[{"id":3668765,"web_url":"http://patchwork.ozlabs.org/comment/3668765/","msgid":"<456faa09-4889-43e2-a35a-449888f9249e@linaro.org>","list_archive_url":null,"date":"2026-03-25T01:39:14","subject":"Re: [PATCH for-11.0] tcg: Pass host-endian values to\n plugin_gen_mem_callbacks_*","submitter":{"id":85798,"url":"http://patchwork.ozlabs.org/api/people/85798/","name":"Pierrick Bouvier","email":"pierrick.bouvier@linaro.org"},"content":"Hi Richard,\n\nOn 3/24/26 5:40 PM, Richard Henderson wrote:\n> If the host does not support swapped-endian loads and stores,\n> then we emulate those within the tcg expanders with explicit\n> bswap operations.\n> \n> However, we were passing values to the plugin interface in\n> the middle of those bswap operations, which meant that we\n> would pass values of the wrong endianness to plugins when\n> running on hosts without swapped-endian loads and stores.\n> \n> Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3351\n> Signed-off-by: Richard Henderson \n> ---\n> \n> Hi Pierrick,\n> \n> On IRC I expressed the opinion that there was an additional\n> big-endian bug with how we treat neg.plugin_mem_value_low,\n> but I now see that isn't true, because of how we adjust the\n> store address in plugin_gen_mem_callbacks_i32.\n>\n\nYes, we store the value directly swapped, so there is no further \ntransformation needed.\n\n> \n> r~\n> ---\n> tcg/tcg-op-ldst.c | 52 ++++++++++++++++++++++++-----------------------\n> 1 file changed, 27 insertions(+), 25 deletions(-)\n> \n> diff --git a/tcg/tcg-op-ldst.c b/tcg/tcg-op-ldst.c\n> index 354d9968f9..22211ccb45 100644\n> --- a/tcg/tcg-op-ldst.c\n> +++ b/tcg/tcg-op-ldst.c\n> @@ -262,9 +262,6 @@ static void tcg_gen_qemu_ld_i32_int(TCGv_i32 val, TCGTemp *addr,\n> addr_new = tci_extend_addr(addr);\n> copy_addr = plugin_maybe_preserve_addr(addr);\n> gen_ldst1(INDEX_op_qemu_ld, TCG_TYPE_I32, tcgv_i32_temp(val), addr_new, oi);\n> - plugin_gen_mem_callbacks_i32(val, copy_addr, addr, orig_oi,\n> - QEMU_PLUGIN_MEM_R);\n> - maybe_free_addr(addr, addr_new);\n> \n> if ((orig_memop ^ memop) & MO_BSWAP) {\n> switch (orig_memop & MO_SIZE) {\n> @@ -280,6 +277,10 @@ static void tcg_gen_qemu_ld_i32_int(TCGv_i32 val, TCGTemp *addr,\n> g_assert_not_reached();\n> }\n> }\n> +\n> + plugin_gen_mem_callbacks_i32(val, copy_addr, addr, orig_oi,\n> + QEMU_PLUGIN_MEM_R);\n> + maybe_free_addr(addr, addr_new);\n> }\n> \n> void tcg_gen_qemu_ld_i32_chk(TCGv_i32 val, TCGTemp *addr, TCGArg idx,\n> @@ -290,10 +291,10 @@ void tcg_gen_qemu_ld_i32_chk(TCGv_i32 val, TCGTemp *addr, TCGArg idx,\n> tcg_gen_qemu_ld_i32_int(val, addr, idx, memop);\n> }\n> \n> -static void tcg_gen_qemu_st_i32_int(TCGv_i32 val, TCGTemp *addr,\n> +static void tcg_gen_qemu_st_i32_int(TCGv_i32 orig_val, TCGTemp *addr,\n> TCGArg idx, MemOp memop)\n> {\n> - TCGv_i32 swap = NULL;\n> + TCGv_i32 val = orig_val;\n> MemOpIdx orig_oi, oi;\n> TCGTemp *addr_new;\n> \n> @@ -302,29 +303,29 @@ static void tcg_gen_qemu_st_i32_int(TCGv_i32 val, TCGTemp *addr,\n> orig_oi = oi = make_memop_idx(memop, idx);\n> \n> if ((memop & MO_BSWAP) && !tcg_target_has_memory_bswap(memop)) {\n> - swap = tcg_temp_ebb_new_i32();\n> + val = tcg_temp_ebb_new_i32();\n> switch (memop & MO_SIZE) {\n> case MO_16:\n> - tcg_gen_bswap16_i32(swap, val, 0);\n> + tcg_gen_bswap16_i32(val, orig_val, 0);\n> break;\n> case MO_32:\n> - tcg_gen_bswap32_i32(swap, val);\n> + tcg_gen_bswap32_i32(val, orig_val);\n> break;\n> default:\n> g_assert_not_reached();\n> }\n> - val = swap;\n> memop &= ~MO_BSWAP;\n> oi = make_memop_idx(memop, idx);\n> }\n> \n> addr_new = tci_extend_addr(addr);\n> gen_ldst1(INDEX_op_qemu_st, TCG_TYPE_I32, tcgv_i32_temp(val), addr_new, oi);\n> - plugin_gen_mem_callbacks_i32(val, NULL, addr, orig_oi, QEMU_PLUGIN_MEM_W);\n> + plugin_gen_mem_callbacks_i32(orig_val, NULL, addr, orig_oi,\n> + QEMU_PLUGIN_MEM_W);\n\nIt works, but it is still not clear to me why the value orig_val (which \nis not swapped and in target-endian order) gets stored swapped correctly \nin neg.plugin_mem_value_low.\n\nI would expect it to be in target-endian order, since \nplugin_gen_mem_callbacks_i32 uses tcg_gen_st_i32(val, env, ... \nneg.plugin_mem_value_low) which does not perform any swap.\n\n> maybe_free_addr(addr, addr_new);\n> \n> - if (swap) {\n> - tcg_temp_free_i32(swap);\n> + if (val != orig_val) {\n> + tcg_temp_free_i32(val);\n> }\n> }\n> \n> @@ -360,9 +361,6 @@ static void tcg_gen_qemu_ld_i64_int(TCGv_i64 val, TCGTemp *addr,\n> addr_new = tci_extend_addr(addr);\n> copy_addr = plugin_maybe_preserve_addr(addr);\n> gen_ld_i64(val, addr_new, oi);\n> - plugin_gen_mem_callbacks_i64(val, copy_addr, addr, orig_oi,\n> - QEMU_PLUGIN_MEM_R);\n> - maybe_free_addr(addr, addr_new);\n> \n> if ((orig_memop ^ memop) & MO_BSWAP) {\n> int flags = (orig_memop & MO_SIGN\n> @@ -382,6 +380,10 @@ static void tcg_gen_qemu_ld_i64_int(TCGv_i64 val, TCGTemp *addr,\n> g_assert_not_reached();\n> }\n> }\n> +\n> + plugin_gen_mem_callbacks_i64(val, copy_addr, addr, orig_oi,\n> + QEMU_PLUGIN_MEM_R);\n> + maybe_free_addr(addr, addr_new);\n> }\n> \n> void tcg_gen_qemu_ld_i64_chk(TCGv_i64 val, TCGTemp *addr, TCGArg idx,\n> @@ -392,10 +394,10 @@ void tcg_gen_qemu_ld_i64_chk(TCGv_i64 val, TCGTemp *addr, TCGArg idx,\n> tcg_gen_qemu_ld_i64_int(val, addr, idx, memop);\n> }\n> \n> -static void tcg_gen_qemu_st_i64_int(TCGv_i64 val, TCGTemp *addr,\n> +static void tcg_gen_qemu_st_i64_int(TCGv_i64 orig_val, TCGTemp *addr,\n> TCGArg idx, MemOp memop)\n> {\n> - TCGv_i64 swap = NULL;\n> + TCGv_i64 val = orig_val;\n> MemOpIdx orig_oi, oi;\n> TCGTemp *addr_new;\n> \n> @@ -404,32 +406,32 @@ static void tcg_gen_qemu_st_i64_int(TCGv_i64 val, TCGTemp *addr,\n> orig_oi = oi = make_memop_idx(memop, idx);\n> \n> if ((memop & MO_BSWAP) && !tcg_target_has_memory_bswap(memop)) {\n> - swap = tcg_temp_ebb_new_i64();\n> + val = tcg_temp_ebb_new_i64();\n> switch (memop & MO_SIZE) {\n> case MO_16:\n> - tcg_gen_bswap16_i64(swap, val, 0);\n> + tcg_gen_bswap16_i64(val, orig_val, 0);\n> break;\n> case MO_32:\n> - tcg_gen_bswap32_i64(swap, val, 0);\n> + tcg_gen_bswap32_i64(val, orig_val, 0);\n> break;\n> case MO_64:\n> - tcg_gen_bswap64_i64(swap, val);\n> + tcg_gen_bswap64_i64(val, orig_val);\n> break;\n> default:\n> g_assert_not_reached();\n> }\n> - val = swap;\n> memop &= ~MO_BSWAP;\n> oi = make_memop_idx(memop, idx);\n> }\n> \n> addr_new = tci_extend_addr(addr);\n> gen_st_i64(val, addr_new, oi);\n> - plugin_gen_mem_callbacks_i64(val, NULL, addr, orig_oi, QEMU_PLUGIN_MEM_W);\n> + plugin_gen_mem_callbacks_i64(orig_val, NULL, addr, orig_oi,\n> + QEMU_PLUGIN_MEM_W);\n> maybe_free_addr(addr, addr_new);\n> \n> - if (swap) {\n> - tcg_temp_free_i64(swap);\n> + if (val != orig_val) {\n> + tcg_temp_free_i64(val);\n> }\n> }\n> \n\nThis solves the problem, thanks!\n\nI'll probably add another patch to document that better in plugin api, \nand remove the additional swapping done in tests/tcg/plugins/mem.c.\n\nReviewed-by: Pierrick Bouvier \nTested-by: Pierrick Bouvier \n\nThanks for the patch,\nPierrick","headers":{"Return-Path":"","X-Original-To":"incoming@patchwork.ozlabs.org","Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=linaro.org header.i=@linaro.org header.a=rsa-sha256\n header.s=google header.b=KUU2H0QK;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; helo=lists.gnu.org;\n envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org;\n receiver=patchwork.ozlabs.org)"],"Received":["from lists.gnu.org (lists.gnu.org [209.51.188.17])\n\t(using TLSv1.2 with cipher ECDHE-ECDSA-AES256-GCM-SHA384 (256/256 bits))\n\t(No client certificate requested)\n\tby legolas.ozlabs.org (Postfix) with ESMTPS id 4fgV2Q1H3Fz1xy1\n\tfor ; Wed, 25 Mar 2026 12:39:42 +1100 (AEDT)","from localhost ([::1] helo=lists1p.gnu.org)\n\tby lists.gnu.org with esmtp (Exim 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PM, Richard Henderson wrote:\n> If the host does not support swapped-endian loads and stores,\n> then we emulate those within the tcg expanders with explicit\n> bswap operations.\n> \n> However, we were passing values to the plugin interface in\n> the middle of those bswap operations, which meant that we\n> would pass values of the wrong endianness to plugins when\n> running on hosts without swapped-endian loads and stores.\n> \n> Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3351\n> Signed-off-by: Richard Henderson \n> ---\n> \n> Hi Pierrick,\n> \n> On IRC I expressed the opinion that there was an additional\n> big-endian bug with how we treat neg.plugin_mem_value_low,\n> but I now see that isn't true, because of how we adjust the\n> store address in plugin_gen_mem_callbacks_i32.\n> \n> \n> r~\n> ---\n> tcg/tcg-op-ldst.c | 52 ++++++++++++++++++++++++-----------------------\n> 1 file changed, 27 insertions(+), 25 deletions(-)\n> \n\nI integrated this commit in a broader series on the same topic:\nhttps://lore.kernel.org/qemu-devel/20260325024252.3369186-1-pierrick.bouvier@linaro.org/T/#t\n\nRegards,\nPierrick","headers":{"Return-Path":"","X-Original-To":"incoming@patchwork.ozlabs.org","Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=linaro.org header.i=@linaro.org header.a=rsa-sha256\n header.s=google header.b=EVvZUPJ7;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; helo=lists.gnu.org;\n envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org;\n receiver=patchwork.ozlabs.org)"],"Received":["from lists.gnu.org (lists.gnu.org [209.51.188.17])\n\t(using TLSv1.2 with cipher ECDHE-ECDSA-AES256-GCM-SHA384 (256/256 bits))\n\t(No client certificate requested)\n\tby legolas.ozlabs.org (Postfix) with ESMTPS id 4fgWVj0n9Jz1xy3\n\tfor ; Wed, 25 Mar 2026 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qemu-devel@nongnu.org","References":"<20260325004052.1026892-1-richard.henderson@linaro.org>","From":"Pierrick Bouvier ","Content-Language":"en-US","Autocrypt":"addr=pierrick.bouvier@linaro.org; keydata=\n xsDNBGK9dgwBDACYuRpR31LD+BnJ0M4b5YnPZKbj+gyu82IDN0MeMf2PGf1sux+1O2ryzmnA\n eOiRCUY9l7IbtPYPHN5YVx+7W3vo6v89I7mL940oYAW8loPZRSMbyCiUeSoiN4gWPXetoNBg\n CJmXbVYQgL5e6rsXoMlwFWuGrBY3Ig8YhEqpuYDkRXj2idO11CiDBT/b8A2aGixnpWV/s+AD\n gUyEVjHU6Z8UervvuNKlRUNE0rUfc502Sa8Azdyda8a7MAyrbA/OI0UnSL1m+pXXCxOxCvtU\n qOlipoCOycBjpLlzjj1xxRci+ssiZeOhxdejILf5LO1gXf6pP+ROdW4ySp9L3dAWnNDcnj6U\n 2voYk7/RpRUTpecvkxnwiOoiIQ7BatjkssFy+0sZOYNbOmoqU/Gq+LeFqFYKDV8gNmAoxBvk\n L6EtXUNfTBjiMHyjA/HMMq27Ja3/Y73xlFpTVp7byQoTwF4p1uZOOXjFzqIyW25GvEekDRF8\n IpYd6/BomxHzvMZ2sQ/VXaMAEQEAAc0uUGllcnJpY2sgQm91dmllciA8cGllcnJpY2suYm91\n dmllckBsaW5hcm8ub3JnPsLBDgQTAQoAOBYhBGa5lOyhT38uWroIH3+QVA0KHNAPBQJivXYM\n AhsDBQsJCAcCBhUKCQgLAgQWAgMBAh4BAheAAAoJEH+QVA0KHNAPX58L/1DYzrEO4TU9ZhJE\n 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plugin_gen_mem_callbacks_*","submitter":{"id":72104,"url":"http://patchwork.ozlabs.org/api/people/72104/","name":"Richard Henderson","email":"richard.henderson@linaro.org"},"content":"On 3/25/26 11:39, Pierrick Bouvier wrote:\n> Hi Richard,\n> \n> On 3/24/26 5:40 PM, Richard Henderson wrote:\n>> If the host does not support swapped-endian loads and stores,\n>> then we emulate those within the tcg expanders with explicit\n>> bswap operations.\n>>\n>> However, we were passing values to the plugin interface in\n>> the middle of those bswap operations, which meant that we\n>> would pass values of the wrong endianness to plugins when\n>> running on hosts without swapped-endian loads and stores.\n>>\n>> Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3351\n>> Signed-off-by: Richard Henderson \n>> ---\n>>\n>> Hi Pierrick,\n>>\n>> On IRC I expressed the opinion that there was an additional\n>> big-endian bug with how we treat neg.plugin_mem_value_low,\n>> but I now see that isn't true, because of how we adjust the\n>> store address in plugin_gen_mem_callbacks_i32.\n>>\n> \n> Yes, we store the value directly swapped, so there is no further transformation needed.\n\nIt's not about storing the value swapped, it's about storing the i32 to the low part of \nthe uint64_t for the host endianness.\n\n> It works, but it is still not clear to me why the value orig_val (which is not swapped and \n> in target-endian order) gets stored swapped correctly in neg.plugin_mem_value_low.\n\nAgain, it is *not* swapped: orig_val is host-endian order, and so is neg.plugin_mem_value_low.\n\n> I'll probably add another patch to document that better in plugin api, and remove the \n> additional swapping done in tests/tcg/plugins/mem.c.\n\nWhat swapping is that?\n\nThere's a variable called \"swapped_value\", but it appears to be mis-named, or a remnant of \nswapping that used to 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","Content-Language":"en-US","In-Reply-To":"<456faa09-4889-43e2-a35a-449888f9249e@linaro.org>","Content-Type":"text/plain; charset=UTF-8; format=flowed","Content-Transfer-Encoding":"7bit","Received-SPF":"pass client-ip=2607:f8b0:4864:20::532;\n envelope-from=richard.henderson@linaro.org; helo=mail-pg1-x532.google.com","X-Spam_score_int":"-20","X-Spam_score":"-2.1","X-Spam_bar":"--","X-Spam_report":"(-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1,\n DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1,\n RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001,\n SPF_PASS=-0.001 autolearn=ham autolearn_force=no","X-Spam_action":"no action","X-BeenThere":"qemu-devel@nongnu.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"qemu development ","List-Unsubscribe":",\n ","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n ","Errors-To":"qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org","Sender":"qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org"}},{"id":3669142,"web_url":"http://patchwork.ozlabs.org/comment/3669142/","msgid":"<1bc4bc8c-4ef7-445f-816f-f76380ee264a@linaro.org>","list_archive_url":null,"date":"2026-03-25T15:15:51","subject":"Re: [PATCH for-11.0] tcg: Pass host-endian values to\n plugin_gen_mem_callbacks_*","submitter":{"id":85798,"url":"http://patchwork.ozlabs.org/api/people/85798/","name":"Pierrick Bouvier","email":"pierrick.bouvier@linaro.org"},"content":"On 3/24/26 9:59 PM, Richard Henderson wrote:\n> On 3/25/26 11:39, Pierrick Bouvier wrote:\n>> Hi Richard,\n>>\n>> On 3/24/26 5:40 PM, Richard Henderson wrote:\n>>> If the host does not support swapped-endian loads and stores,\n>>> then we emulate those within the tcg expanders with explicit\n>>> bswap operations.\n>>>\n>>> However, we were passing values to the plugin interface in\n>>> the middle of those bswap operations, which meant that we\n>>> would pass values of the wrong endianness to plugins when\n>>> running on hosts without swapped-endian loads and stores.\n>>>\n>>> Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3351\n>>> Signed-off-by: Richard Henderson \n>>> ---\n>>>\n>>> Hi Pierrick,\n>>>\n>>> On IRC I expressed the opinion that there was an additional\n>>> big-endian bug with how we treat neg.plugin_mem_value_low,\n>>> but I now see that isn't true, because of how we adjust the\n>>> store address in plugin_gen_mem_callbacks_i32.\n>>>\n>>\n>> Yes, we store the value directly swapped, so there is no further transformation needed.\n>\n> It's not about storing the value swapped, it's about storing the i32 to the low part of\n> the uint64_t for the host endianness.\n>\n\nI finally realized the orig_value we had is already in host-endian \norder, while I was assuming it was in target-endian order. Thus the \nconfusion in our conversion. All good now.\n\n>> It works, but it is still not clear to me why the value orig_val (which is not swapped and\n>> in target-endian order) gets stored swapped correctly in neg.plugin_mem_value_low.\n> \n> Again, it is *not* swapped: orig_val is host-endian order, and so is neg.plugin_mem_value_low.\n> \n>> I'll probably add another patch to document that better in plugin api, and remove the\n>> additional swapping done in tests/tcg/plugins/mem.c.\n> \n> What swapping is that?\n>\n\nIt tracks memory regions we accessed, so which byte was written matters \nin this case, thus the need to swap to target-endian order.\n\n> There's a variable called \"swapped_value\", but it appears to be mis-named, or a remnant of\n> swapping that used to occur.\n>\n\nIt's basically the value in target-endian order. FROM_BE should to TO_BE \nas well, even though both macros do exactly the same (FROM or TO acting \nas documentation to express the intent).\n\n> \n> r~","headers":{"Return-Path":"","X-Original-To":"incoming@patchwork.ozlabs.org","Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=linaro.org header.i=@linaro.org header.a=rsa-sha256\n header.s=google header.b=kvuzR9KT;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; helo=lists.gnu.org;\n envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org;\n receiver=patchwork.ozlabs.org)"],"Received":["from lists.gnu.org (lists.gnu.org [209.51.188.17])\n\t(using TLSv1.2 with cipher ECDHE-ECDSA-AES256-GCM-SHA384 (256/256 bits))\n\t(No client certificate requested)\n\tby legolas.ozlabs.org (Postfix) with ESMTPS id 4fgr985Dnwz1xy3\n\tfor ; Thu, 26 Mar 2026 02:16:43 +1100 (AEDT)","from localhost ([::1] helo=lists1p.gnu.org)\n\tby lists.gnu.org with esmtp (Exim 4.90_1)\n\t(envelope-from )\n\tid 1w5Pxi-0003xr-SM; 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