最近在学习 linux driver 时, 在 qemu 上使用 aarch64 架构来跑 Image, 在想使用单步跑看看 driver 的某些执行路径时, 发现给 driver 添加 O0 编译时会有很多错误.
比如在 Linux-6.10 中, 我们在如下修改状态下, 使用命令 make LLVM=1 ARCH=arm64 defconfig && make LLVM=1 ARCH=arm64 Image -j12 编译的时候
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| diff --git a/arch/arm64/configs/defconfig b/arch/arm64/configs/defconfig
index 2c7bf4da0..857020b8c 100644
--- a/arch/arm64/configs/defconfig
+++ b/arch/arm64/configs/defconfig
@@ -116,7 +116,7 @@ CONFIG_ACPI_APEI_MEMORY_FAILURE=y
CONFIG_ACPI_APEI_EINJ=y
CONFIG_VIRTUALIZATION=y
CONFIG_KVM=y
-CONFIG_JUMP_LABEL=y
+# CONFIG_JUMP_LABEL is not set
CONFIG_MODULES=y
CONFIG_MODULE_UNLOAD=y
CONFIG_IOSCHED_BFQ=y
diff --git a/drivers/Makefile b/drivers/Makefile
index fe9ceb0d2..f60455123 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -193,3 +193,5 @@ obj-$(CONFIG_CDX_BUS) += cdx/
obj-$(CONFIG_DPLL) += dpll/
obj-$(CONFIG_S390) += s390/
+
+subdir-ccflags-y += -O0
|
会报出汗多的 error: invalid operand for inline asm constraint 'i' 错误. 下面我们就来探究下这个问题.
很多出错都指向了下面这个函数:
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| static __always_inline bool
alternative_has_cap_likely(const unsigned long cpucap)
{
if (!cpucap_is_possible(cpucap))
return false;
asm goto(
ALTERNATIVE_CB("b %l[l_no]", %[cpucap], alt_cb_patch_nops)
:
: [cpucap] "i" (cpucap)
:
: l_no);
return true;
l_no:
return false;
}
|
其传入了一个 cpucap, 在调用这个内联函数的时候, 传入给 cpucap 的都是一个编译时常量, 比如
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| #define ARM64_ALWAYS_BOOT 0
alternative_has_cap_likely(ARM64_ALWAYS_BOOT);
|
这样在调用的地方, 将这个内联函数展开, 此时 cpucap 就是一个编译时的常量. 因此在内嵌汇编 asm 块中可以将这个 cpucap 以 “i” 类型输入参数传递.
但是当我们关闭了优化(比如用 O0)编译的时候, 这个内联函数就不会被内联展开, 此时 cpucap 就是一个变量了, 变量是不能作为 “i” 类型输入参数传递给 asm 块的. 因此就会报错.
要解决这个问题, 我们需要修改下这种类型的内联函数的实现, 比如将这种内联函数修改成宏. 不过这个函数内部存在跳转. 我们修改的宏内部最好不要有这种跳转, 避免跳转标签发生冲突, 可以按照如下的方式来修改:
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| #define alternative_has_cap_likely(cpucap) \
({ \
int ret = true; \
if (cpucap_is_possible(cpucap)) { \
asm(ALTERNATIVE_CB("mov %w[ret], #0", %[_cpucap], \
alt_cb_patch_nops) \
: [ret] "+r"(ret) \
: [_cpucap] "i"(cpucap) \
:); \
} else { \
ret = false; \
} \
ret; \
})
|
修改之后, 我们将 goto 这个需求去掉了. 但是实现了同样的功能. 由于此时我们将内联函数改为了宏, 也就避开了 O0 编译时内联函数不展开的问题了.
最终的修改 patch 如下:
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| diff --git a/arch/arm64/configs/defconfig b/arch/arm64/configs/defconfig
index 2c7bf4da0..4b430913c 100644
--- a/arch/arm64/configs/defconfig
+++ b/arch/arm64/configs/defconfig
@@ -116,7 +116,6 @@ CONFIG_ACPI_APEI_MEMORY_FAILURE=y
CONFIG_ACPI_APEI_EINJ=y
CONFIG_VIRTUALIZATION=y
CONFIG_KVM=y
-CONFIG_JUMP_LABEL=y
CONFIG_MODULES=y
CONFIG_MODULE_UNLOAD=y
CONFIG_IOSCHED_BFQ=y
@@ -563,6 +562,7 @@ CONFIG_SPI_SUN6I=y
CONFIG_SPI_TEGRA210_QUAD=m
CONFIG_SPI_TEGRA114=m
CONFIG_SPI_SPIDEV=m
+CONFIG_SPI_SLAVE=y
CONFIG_SPMI=y
CONFIG_SPMI_MTK_PMIF=m
CONFIG_PINCTRL_DA9062=m
diff --git a/arch/arm64/include/asm/alternative-macros.h b/arch/arm64/include/asm/alternative-macros.h
index d328f549b..17892cb57 100644
--- a/arch/arm64/include/asm/alternative-macros.h
+++ b/arch/arm64/include/asm/alternative-macros.h
@@ -223,41 +223,32 @@ alternative_endif
#include <linux/types.h>
-static __always_inline bool
-alternative_has_cap_likely(const unsigned long cpucap)
-{
- if (!cpucap_is_possible(cpucap))
- return false;
-
- asm goto(
- ALTERNATIVE_CB("b %l[l_no]", %[cpucap], alt_cb_patch_nops)
- :
- : [cpucap] "i" (cpucap)
- :
- : l_no);
-
- return true;
-l_no:
- return false;
-}
-
-static __always_inline bool
-alternative_has_cap_unlikely(const unsigned long cpucap)
-{
- if (!cpucap_is_possible(cpucap))
- return false;
-
- asm goto(
- ALTERNATIVE("nop", "b %l[l_yes]", %[cpucap])
- :
- : [cpucap] "i" (cpucap)
- :
- : l_yes);
-
- return false;
-l_yes:
- return true;
-}
+#define alternative_has_cap_likely(cpucap) \
+ ({ \
+ int ret = true; \
+ if (cpucap_is_possible(cpucap)) { \
+ asm(ALTERNATIVE_CB("mov %w[ret], #0", %[_cpucap], \
+ alt_cb_patch_nops) \
+ : [ret] "+r"(ret) \
+ : [_cpucap] "i"(cpucap) \
+ :); \
+ } else { \
+ ret = false; \
+ } \
+ ret; \
+ })
+
+#define alternative_has_cap_unlikely(cpucap) \
+ ({ \
+ int ret = false; \
+ if (cpucap_is_possible(cpucap)) { \
+ asm(ALTERNATIVE("nop", "mov %w[ret], #1", %[_cpucap]) \
+ : [ret] "+r"(ret) \
+ : [_cpucap] "i"(cpucap) \
+ :); \
+ } \
+ ret; \
+ })
#endif
diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 8b904a757..aa26a1152 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -475,13 +475,12 @@ static __always_inline bool cpus_have_cap(unsigned int num)
*
* @num must be a compile-time constant.
*/
-static __always_inline bool cpus_have_final_boot_cap(int num)
-{
- if (boot_capabilities_finalized())
- return alternative_has_cap_unlikely(num);
- else
- BUG();
-}
+#define cpus_have_final_boot_cap(num) \
+ ({ \
+ if (!boot_capabilities_finalized()) \
+ BUG(); \
+ alternative_has_cap_unlikely(num); \
+ })
-static __always_inline bool cpus_have_final_cap(int num)
-{
- if (system_capabilities_finalized())
- return alternative_has_cap_unlikely(num);
- else
- BUG();
-}
+#define cpus_have_final_cap(num) \
+ ({ \
+ if (!system_capabilities_finalized()) \
+ BUG(); \
+ alternative_has_cap_unlikely(num); \
+ })
static inline int __attribute_const__
cpuid_feature_extract_signed_field_width(u64 features, int field, int width)
diff --git a/drivers/Makefile b/drivers/Makefile
index fe9ceb0d2..f60455123 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -193,3 +193,5 @@ obj-$(CONFIG_CDX_BUS) += cdx/
obj-$(CONFIG_DPLL) += dpll/
obj-$(CONFIG_S390) += s390/
+
+subdir-ccflags-y += -O0
diff --git a/drivers/firmware/Makefile b/drivers/firmware/Makefile
index 7a8d486e7..342f9dadc 100644
--- a/drivers/firmware/Makefile
+++ b/drivers/firmware/Makefile
@@ -36,3 +36,5 @@ obj-y += qcom/
obj-y += smccc/
obj-y += tegra/
obj-y += xilinx/
+
+subdir-ccflags-y += -Og
diff --git a/drivers/net/ethernet/Makefile b/drivers/net/ethernet/Makefile
index 0d872d4ef..baff0f30c 100644
--- a/drivers/net/ethernet/Makefile
+++ b/drivers/net/ethernet/Makefile
@@ -104,3 +104,5 @@ obj-$(CONFIG_NET_VENDOR_XILINX) += xilinx/
obj-$(CONFIG_NET_VENDOR_XIRCOM) += xircom/
obj-$(CONFIG_NET_VENDOR_SYNOPSYS) += synopsys/
obj-$(CONFIG_NET_VENDOR_PENSANDO) += pensando/
+
+subdir-ccflags-y += -Og
diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index 79edd5b5e..dba21fa6c 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -509,7 +509,7 @@ static inline bool lockdep_tcf_proto_is_locked(struct tcf_proto *tp)
static inline void qdisc_cb_private_validate(const struct sk_buff *skb, int sz)
{
- struct qdisc_skb_cb *qcb;
+ struct qdisc_skb_cb *qcb __attribute__((unused));
BUILD_BUG_ON(sizeof(skb->cb) < sizeof(*qcb));
BUILD_BUG_ON(sizeof(qcb->data) < sz);
|