Hi Russell and Guenter, Le 03/03/2024 à 16:26, Guenter Roeck a écrit : > On 3/3/24 02:20, Christophe Leroy wrote: >> >> >> Le 01/03/2024 à 19:32, Guenter Roeck a écrit : >>> This leaves the mps2-an385:mps2_defconfig crash, which is avoided by >>> this patch. >>> My understanding, which may be wrong, is that arm images with thumb >>> instructions >>> do not support unaligned accesses (maybe I should say do not support >>> unaligned >>> accesses with the mps2-an385 qemu emulation; I did not test with real >>> hardware, >>> after all). ... >> >> Can you tell how to proceed ? >> > > You can't run it directly. mps2-an385 is one of the platforms where > the qemu maintainers insisted that qemu shall not initialize the CPU. > You have to provide a shim such as > https://github.com/groeck/linux-build-test/blob/master/rootfs/arm/mps2-boot.axf > as bios. You also have to provide the dtb file. > > On top of that, you would need a customized version of qemu which > actually reads the command line, the bios file, and the dtb. See > https://github.com/groeck/linux-build-test/tree/master/qemu > branch v8.2.1-local or v8.1.5-local. > Many thanks for your guidance. So, I did the test and what I can say: ip_fast_csum() works whatever the alignment is. csum_ipv6_magic() is the problem with unaligned ipv6 source or destination addresses: [ 0.503757] KTAP version 1 [ 0.503854] 1..1 [ 0.504156] KTAP version 1 [ 0.504251] # Subtest: checksum [ 0.504563] # module: checksum_kunit [ 0.504730] 1..5 [ 0.546418] ok 1 test_csum_fixed_random_inputs [ 0.627853] ok 2 test_csum_all_carry_inputs [ 0.704918] ok 3 test_csum_no_carry_inputs [ 0.705845] ok 4 test_ip_fast_csum [ 0.706320] [ 0.706320] Unhandled exception: IPSR = 00000006 LR = fffffff1 [ 0.706796] CPU: 0 PID: 28 Comm: kunit_try_catch Tainted: G N 6.8.0-rc1-00609-g9c0b7a2e25f0 #649 [ 0.707177] Hardware name: Generic DT based system [ 0.707400] PC is at __csum_ipv6_magic+0x8/0xb4 [ 0.708170] LR is at test_csum_ipv6_magic+0x3d/0xa4 [ 0.708415] pc : [<211b0da8>] lr : [<210e3bf5>] psr: 0100020b [ 0.708692] sp : 2153debc ip : 46c7f0d2 fp : 00000000 [ 0.708919] r10: 00000000 r9 : 2141dc48 r8 : 211e0e20 [ 0.709148] r7 : 00003085 r6 : 00000001 r5 : 2141dd24 r4 : 211e0c2e [ 0.709422] r3 : 2c000000 r2 : 1ac7f0d2 r1 : 211e0c19 r0 : 211e0c09 [ 0.709704] xPSR: 0100020b I don't know much about ARM instruction set, seems like the ldr instruction used in ip_fast_csum() doesn't mind unaligned accesses while ldmia instruction used in csum_ipv6_magic() minds. Or is it a wrong behaviour of QEMU ? If I change the test as follows to only use word aligned IPv6 addresses, it works: diff --git a/lib/checksum_kunit.c b/lib/checksum_kunit.c index 225bb7701460..4d86fc8ccd78 100644 --- a/lib/checksum_kunit.c +++ b/lib/checksum_kunit.c @@ -607,7 +607,7 @@ static void test_csum_ipv6_magic(struct kunit *test) const int csum_offset = sizeof(struct in6_addr) + sizeof(struct in6_addr) + sizeof(int) + sizeof(char); - for (int i = 0; i < NUM_IPv6_TESTS; i++) { + for (int i = 0; i < NUM_IPv6_TESTS; i += 4) { saddr = (const struct in6_addr *)(random_buf + i); daddr = (const struct in6_addr *)(random_buf + i + daddr_offset); If I change csum_ipv6_magic() as follows to use instruction ldr instead of ldmia, it also works without any change to the test: diff --git a/arch/arm/lib/csumipv6.S b/arch/arm/lib/csumipv6.S index 3559d515144c..a312d0836b95 100644 --- a/arch/arm/lib/csumipv6.S +++ b/arch/arm/lib/csumipv6.S @@ -12,12 +12,18 @@ ENTRY(__csum_ipv6_magic) str lr, [sp, #-4]! adds ip, r2, r3 - ldmia r1, {r1 - r3, lr} + ldr r2, [r1], #4 + ldr r3, [r1], #4 + ldr lr, [r1], #4 + ldr r1, [r1] adcs ip, ip, r1 adcs ip, ip, r2 adcs ip, ip, r3 adcs ip, ip, lr - ldmia r0, {r0 - r3} + ldr r1, [r0], #4 + ldr r2, [r0], #4 + ldr r3, [r0], #4 + ldr r0, [r0] adcs r0, ip, r0 adcs r0, r0, r1 adcs r0, r0, r2 So now we are back to the initial question, should checksumming on unaligned addresses be supported or not ? Russell I understand from previous answers from you that half-word alignment should be supported, in that case should ARM version of csum_ipv6_magic() be modified ? In that case can you propose the most optimised fix ? If not, then the test has to be fixed to only use word-aligned IPv6 addresses. Thanks Christophe
