From 936fda4d771fdc51d3640bdb0cc8ceec14165730 Mon Sep 17 00:00:00 2001 From: Fabiano Rosas Date: Mon, 22 Feb 2021 16:40:35 -0300 Subject: [PATCH] target/ppc: Fix bcdsub. emulation when result overflows The commit d03b174a83 (target/ppc: simplify bcdadd/sub functions) meant to simplify some of the code but it inadvertently altered the way the CR6 field is set after the operation has overflowed. The CR6 bits are set based on the *unbounded* result of the operation, so we need to look at the result before returning from bcd_add_mag, otherwise we will look at 0 when it overflows. Consider the following subtraction: v0 = 0x9999999999999999999999999999999c (maximum positive BCD value) v1 = 0x0000000000000000000000000000001d (negative one BCD value) bcdsub. v0,v0,v1,0 The Power ISA 2.07B says: If the unbounded result is greater than zero, do the following. If PS=0, the sign code of the result is set to 0b1100. If PS=1, the sign code of the result is set to 0b1111. If the operation overflows, CR field 6 is set to 0b0101. Otherwise, CR field 6 is set to 0b0100. POWER9 hardware: vr0 = 0x0000000000000000000000000000000c (positive zero BCD value) cr6 = 0b0101 (0x5) (positive, overflow) QEMU: vr0 = 0x0000000000000000000000000000000c (positive zero BCD value) cr6 = 0b0011 (0x3) (zero, overflow) <--- wrong This patch reverts the part of d03b174a83 that introduced the problem and adds a test-case to avoid further regressions: before: $ make run-tcg-tests-ppc64le-linux-user (...) TEST bcdsub on ppc64le bcdsub: qemu/tests/tcg/ppc64le/bcdsub.c:58: test_bcdsub_gt: Assertion `(cr >> 4) == ((1 << 2) | (1 << 0))' failed. Fixes: d03b174a83 (target/ppc: simplify bcdadd/sub functions) Reported-by: Paul Clarke Signed-off-by: Fabiano Rosas Message-Id: <20210222194035.2723056-1-farosas@linux.ibm.com> Signed-off-by: David Gibson --- target/ppc/int_helper.c | 13 ++- tests/tcg/configure.sh | 6 ++ tests/tcg/ppc64/Makefile.target | 13 +++ tests/tcg/ppc64le/Makefile.target | 12 +++ tests/tcg/ppc64le/bcdsub.c | 130 ++++++++++++++++++++++++++++++ 5 files changed, 171 insertions(+), 3 deletions(-) create mode 100644 tests/tcg/ppc64/Makefile.target create mode 100644 tests/tcg/ppc64le/Makefile.target create mode 100644 tests/tcg/ppc64le/bcdsub.c diff --git a/target/ppc/int_helper.c b/target/ppc/int_helper.c index 0b682a1f94..429de28494 100644 --- a/target/ppc/int_helper.c +++ b/target/ppc/int_helper.c @@ -2175,14 +2175,17 @@ static int bcd_cmp_mag(ppc_avr_t *a, ppc_avr_t *b) return 0; } -static void bcd_add_mag(ppc_avr_t *t, ppc_avr_t *a, ppc_avr_t *b, int *invalid, +static int bcd_add_mag(ppc_avr_t *t, ppc_avr_t *a, ppc_avr_t *b, int *invalid, int *overflow) { int carry = 0; int i; + int is_zero = 1; + for (i = 1; i <= 31; i++) { uint8_t digit = bcd_get_digit(a, i, invalid) + bcd_get_digit(b, i, invalid) + carry; + is_zero &= (digit == 0); if (digit > 9) { carry = 1; digit -= 10; @@ -2194,6 +2197,7 @@ static void bcd_add_mag(ppc_avr_t *t, ppc_avr_t *a, ppc_avr_t *b, int *invalid, } *overflow = carry; + return is_zero; } static void bcd_sub_mag(ppc_avr_t *t, ppc_avr_t *a, ppc_avr_t *b, int *invalid, @@ -2225,14 +2229,15 @@ uint32_t helper_bcdadd(ppc_avr_t *r, ppc_avr_t *a, ppc_avr_t *b, uint32_t ps) int sgnb = bcd_get_sgn(b); int invalid = (sgna == 0) || (sgnb == 0); int overflow = 0; + int zero = 0; uint32_t cr = 0; ppc_avr_t result = { .u64 = { 0, 0 } }; if (!invalid) { if (sgna == sgnb) { result.VsrB(BCD_DIG_BYTE(0)) = bcd_preferred_sgn(sgna, ps); - bcd_add_mag(&result, a, b, &invalid, &overflow); - cr = bcd_cmp_zero(&result); + zero = bcd_add_mag(&result, a, b, &invalid, &overflow); + cr = (sgna > 0) ? CRF_GT : CRF_LT; } else { int magnitude = bcd_cmp_mag(a, b); if (magnitude > 0) { @@ -2255,6 +2260,8 @@ uint32_t helper_bcdadd(ppc_avr_t *r, ppc_avr_t *a, ppc_avr_t *b, uint32_t ps) cr = CRF_SO; } else if (overflow) { cr |= CRF_SO; + } else if (zero) { + cr |= CRF_EQ; } *r = result; diff --git a/tests/tcg/configure.sh b/tests/tcg/configure.sh index 36b8a73a54..ce304f4933 100755 --- a/tests/tcg/configure.sh +++ b/tests/tcg/configure.sh @@ -251,6 +251,12 @@ for target in $target_list; do echo "CROSS_CC_HAS_ARMV8_MTE=y" >> $config_target_mak fi ;; + ppc*) + if do_compiler "$target_compiler" $target_compiler_cflags \ + -mpower8-vector -o $TMPE $TMPC; then + echo "CROSS_CC_HAS_POWER8_VECTOR=y" >> $config_target_mak + fi + ;; esac enabled_cross_compilers="$enabled_cross_compilers $target_compiler" diff --git a/tests/tcg/ppc64/Makefile.target b/tests/tcg/ppc64/Makefile.target new file mode 100644 index 0000000000..0c6a4585fc --- /dev/null +++ b/tests/tcg/ppc64/Makefile.target @@ -0,0 +1,13 @@ +# -*- Mode: makefile -*- +# +# ppc64 specific tweaks + +VPATH += $(SRC_PATH)/tests/tcg/ppc64 +VPATH += $(SRC_PATH)/tests/tcg/ppc64le + +ifneq ($(DOCKER_IMAGE)$(CROSS_CC_HAS_POWER8_VECTOR),) +PPC64_TESTS=bcdsub +endif +bcdsub: CFLAGS += -mpower8-vector + +TESTS += $(PPC64_TESTS) diff --git a/tests/tcg/ppc64le/Makefile.target b/tests/tcg/ppc64le/Makefile.target new file mode 100644 index 0000000000..1acfcff94a --- /dev/null +++ b/tests/tcg/ppc64le/Makefile.target @@ -0,0 +1,12 @@ +# -*- Mode: makefile -*- +# +# ppc64le specific tweaks + +VPATH += $(SRC_PATH)/tests/tcg/ppc64le + +ifneq ($(DOCKER_IMAGE)$(CROSS_CC_HAS_POWER8_VECTOR),) +PPC64LE_TESTS=bcdsub +endif +bcdsub: CFLAGS += -mpower8-vector + +TESTS += $(PPC64LE_TESTS) diff --git a/tests/tcg/ppc64le/bcdsub.c b/tests/tcg/ppc64le/bcdsub.c new file mode 100644 index 0000000000..8c188cae6d --- /dev/null +++ b/tests/tcg/ppc64le/bcdsub.c @@ -0,0 +1,130 @@ +#include +#include +#include + +#define CRF_LT (1 << 3) +#define CRF_GT (1 << 2) +#define CRF_EQ (1 << 1) +#define CRF_SO (1 << 0) +#define UNDEF 0 + +#define BCDSUB(vra, vrb, ps) \ + asm ("bcdsub. %1,%2,%3,%4;" \ + "mfocrf %0,0b10;" \ + : "=r" (cr), "=v" (vrt) \ + : "v" (vra), "v" (vrb), "i" (ps) \ + : ); + +#define TEST(vra, vrb, ps, exp_res, exp_cr6) \ + do { \ + __int128 vrt = 0; \ + int cr = 0; \ + BCDSUB(vra, vrb, ps); \ + if (exp_res) \ + assert(vrt == exp_res); \ + assert((cr >> 4) == exp_cr6); \ + } while (0) + + +/* + * Unbounded result is equal to zero: + * sign = (PS) ? 0b1111 : 0b1100 + * CR6 = 0b0010 + */ +void test_bcdsub_eq(void) +{ + __int128 a, b; + + /* maximum positive BCD value */ + a = b = (((__int128) 0x9999999999999999) << 64 | 0x999999999999999c); + + TEST(a, b, 0, 0xc, CRF_EQ); + TEST(a, b, 1, 0xf, CRF_EQ); +} + +/* + * Unbounded result is greater than zero: + * sign = (PS) ? 0b1111 : 0b1100 + * CR6 = (overflow) ? 0b0101 : 0b0100 + */ +void test_bcdsub_gt(void) +{ + __int128 a, b, c; + + /* maximum positive BCD value */ + a = (((__int128) 0x9999999999999999) << 64 | 0x999999999999999c); + + /* negative one BCD value */ + b = (__int128) 0x1d; + + TEST(a, b, 0, 0xc, (CRF_GT | CRF_SO)); + TEST(a, b, 1, 0xf, (CRF_GT | CRF_SO)); + + c = (((__int128) 0x9999999999999999) << 64 | 0x999999999999998c); + + TEST(c, b, 0, a, CRF_GT); + TEST(c, b, 1, (a | 0x3), CRF_GT); +} + +/* + * Unbounded result is less than zero: + * sign = 0b1101 + * CR6 = (overflow) ? 0b1001 : 0b1000 + */ +void test_bcdsub_lt(void) +{ + __int128 a, b; + + /* positive zero BCD value */ + a = (__int128) 0xc; + + /* positive one BCD value */ + b = (__int128) 0x1c; + + TEST(a, b, 0, 0x1d, CRF_LT); + TEST(a, b, 1, 0x1d, CRF_LT); + + /* maximum negative BCD value */ + a = (((__int128) 0x9999999999999999) << 64 | 0x999999999999999d); + + /* positive one BCD value */ + b = (__int128) 0x1c; + + TEST(a, b, 0, 0xd, (CRF_LT | CRF_SO)); + TEST(a, b, 1, 0xd, (CRF_LT | CRF_SO)); +} + +void test_bcdsub_invalid(void) +{ + __int128 a, b; + + /* positive one BCD value */ + a = (__int128) 0x1c; + b = 0xf00; + + TEST(a, b, 0, UNDEF, CRF_SO); + TEST(a, b, 1, UNDEF, CRF_SO); + + TEST(b, a, 0, UNDEF, CRF_SO); + TEST(b, a, 1, UNDEF, CRF_SO); + + a = 0xbad; + + TEST(a, b, 0, UNDEF, CRF_SO); + TEST(a, b, 1, UNDEF, CRF_SO); +} + +int main(void) +{ + struct sigaction action; + + action.sa_handler = _exit; + sigaction(SIGABRT, &action, NULL); + + test_bcdsub_eq(); + test_bcdsub_gt(); + test_bcdsub_lt(); + test_bcdsub_invalid(); + + return 0; +}