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Wed, 26 Feb 2025 08:02:34 -0800 (PST) Message-ID: <93007262-7e30-40c1-8d8f-3c9ef9d59673@suse.com> Date: Wed, 26 Feb 2025 17:02:33 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: [PATCH v8 6/6] common: honor CONFIG_CC_SPLIT_SECTIONS also for assembly functions From: Jan Beulich To: "xen-devel@lists.xenproject.org" Cc: Julien Grall , Stefano Stabellini , Volodymyr Babchuk , Bertrand Marquis , Michal Orzel , Andrew Cooper , =?utf-8?q?Roger_Pau_Monn=C3=A9?= , Anthony PERARD References: Content-Language: en-US Autocrypt: addr=jbeulich@suse.com; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL In-Reply-To: Leverage the new infrastructure in xen/linkage.h to also switch to per- function sections (when configured), deriving the specific name from the "base" section in use at the time FUNC() is invoked. Signed-off-by: Jan Beulich --- TBD: Since we use .subsection in UNLIKELY_START(), a perhaps not really wanted side effect of this change is that respective out-of-line code now moves much closer to its original (invoking) code. TBD: Of course something with the same overall effect, but less impactful might do in Config.mk. E.g. $(filter-out -D%,$(3)) instead of $(firstword (3)). In fact Roger wants the detection to be in Kconfig, for LIVEPATCH to depend on it. Yet the whole underlying discussion there imo would first need settling (and therefore reviving). Note that we'd need to split DATA() in order to separate r/w, r/o, and BSS contributions. Further splitting might be needed to also support more advanced attributes (e.g. merge), hence why this isn't done right here. Sadly while a new section's name can be derived from the presently in use, its attributes cannot be. Perhaps the only thing we can do is give DATA() a 2nd mandatory parameter. Then again I guess most data definitions could be moved to C anyway. An alternative to the "override" in arm64/head.S would be to use LABEL{,_LOCAL}() instead of FUNC{,_LOCAL}() there. Yet that would also lose the type information then. Question is whether the annotated ranges really are "functions" in whichever wide or narrow sense. --- v7: Override SYM_PUSH_SECTION() in arch/x86/indirect-thunk.S. Re-base, notably to deal with fallout from fba250ae604e ("xen/arm64: head: Add missing code symbol annotations"). v6: Deal with x86'es entry_PF() and entry_int82() falling through to the next "function". Re-base. v5: Re-base over changes earlier in the series. v4: Re-base. v2: Make detection properly fail on old gas (by adjusting cc-option-add-closure). --- a/Config.mk +++ b/Config.mk @@ -102,7 +102,7 @@ cc-option = $(shell if $(1) $(2:-Wno-%=- # Usage: $(call cc-option-add CFLAGS,CC,-march=winchip-c6) cc-option-add = $(eval $(call cc-option-add-closure,$(1),$(2),$(3))) define cc-option-add-closure - ifneq ($$(call cc-option,$$($(2)),$(3),n),n) + ifneq ($$(call cc-option,$$($(2)),$(firstword $(3)),n),n) $(1) += $(3) endif endef --- a/xen/Makefile +++ b/xen/Makefile @@ -415,6 +415,9 @@ AFLAGS += -D__ASSEMBLY__ $(call cc-option-add,AFLAGS,CC,-Wa$$(comma)--noexecstack) +# Check to see whether the assembler supports the --sectname-subst option. +$(call cc-option-add,AFLAGS,CC,-Wa$$(comma)--sectname-subst -DHAVE_AS_SECTNAME_SUBST) + LDFLAGS-$(call ld-option,--warn-rwx-segments) += --no-warn-rwx-segments CFLAGS += $(CFLAGS-y) --- a/xen/arch/arm/arm64/head.S +++ b/xen/arch/arm/arm64/head.S @@ -28,6 +28,14 @@ #include #endif +/* + * Code here is, at least in part, ordering sensitive. Annotations + * from xen/linkage.h therefore may not switch sections (honoring + * CONFIG_CC_SPLIT_SECTIONS). Override the respective macro. + */ +#undef SYM_PUSH_SECTION +#define SYM_PUSH_SECTION(name, attr) + #define __HEAD_FLAG_PAGE_SIZE ((PAGE_SHIFT - 10) / 2) #define __HEAD_FLAG_PHYS_BASE 1 --- a/xen/arch/arm/xen.lds.S +++ b/xen/arch/arm/xen.lds.S @@ -140,6 +140,9 @@ SECTIONS .init.text : { _sinittext = .; *(.init.text) +#ifdef CONFIG_CC_SPLIT_SECTIONS + *(.init.text.*) +#endif _einittext = .; . = ALIGN(PAGE_SIZE); /* Avoid mapping alt insns executable */ *(.altinstr_replacement) --- a/xen/arch/ppc/xen.lds.S +++ b/xen/arch/ppc/xen.lds.S @@ -103,6 +103,9 @@ SECTIONS DECL_SECTION(.init.text) { _sinittext = .; *(.init.text) +#ifdef CONFIG_CC_SPLIT_SECTIONS + *(.init.text.*) +#endif _einittext = .; . = ALIGN(PAGE_SIZE); /* Avoid mapping alt insns executable */ } :text --- a/xen/arch/riscv/xen.lds.S +++ b/xen/arch/riscv/xen.lds.S @@ -98,6 +98,9 @@ SECTIONS .init.text : { _sinittext = .; *(.init.text) +#ifdef CONFIG_CC_SPLIT_SECTIONS + *(.init.text.*) +#endif _einittext = .; . = ALIGN(PAGE_SIZE); /* Avoid mapping alt insns executable */ } :text --- a/xen/arch/x86/indirect-thunk.S +++ b/xen/arch/x86/indirect-thunk.S @@ -11,6 +11,10 @@ #include +/* Section placement is done explicitly here; override the respective macro. */ +#undef SYM_PUSH_SECTION +#define SYM_PUSH_SECTION(name, attr) + .macro IND_THUNK_RETPOLINE reg:req call 1f int3 --- a/xen/arch/x86/x86_64/compat/entry.S +++ b/xen/arch/x86/x86_64/compat/entry.S @@ -31,6 +31,9 @@ FUNC(entry_int82) mov %rsp, %rdi call do_entry_int82 +#ifdef CONFIG_CC_SPLIT_SECTIONS + jmp compat_test_all_events +#endif END(entry_int82) /* %rbx: struct vcpu */ --- a/xen/arch/x86/x86_64/entry.S +++ b/xen/arch/x86/x86_64/entry.S @@ -771,6 +771,9 @@ END(common_interrupt) FUNC(entry_PF) ENDBR64 movb $X86_EXC_PF, EFRAME_entry_vector(%rsp) +#ifdef CONFIG_CC_SPLIT_SECTIONS + jmp handle_exception +#endif END(entry_PF) /* No special register assumptions. */ FUNC(handle_exception, 0) @@ -1084,8 +1087,11 @@ FUNC(entry_NMI) ENDBR64 pushq $0 movb $X86_EXC_NMI, EFRAME_entry_vector(%rsp) +#ifdef CONFIG_CC_SPLIT_SECTIONS + jmp handle_ist_exception +#endif END(entry_NMI) - +/* No special register assumptions. */ FUNC(handle_ist_exception) ALTERNATIVE "", clac, X86_FEATURE_XEN_SMAP SAVE_ALL --- a/xen/arch/x86/xen.lds.S +++ b/xen/arch/x86/xen.lds.S @@ -83,6 +83,9 @@ SECTIONS . = ALIGN(PAGE_SIZE); _stextentry = .; *(.text.entry) +#ifdef CONFIG_CC_SPLIT_SECTIONS + *(.text.entry.*) +#endif . = ALIGN(PAGE_SIZE); _etextentry = .; @@ -202,6 +205,9 @@ SECTIONS #endif _sinittext = .; *(.init.text) +#ifdef CONFIG_CC_SPLIT_SECTIONS + *(.init.text.*) +#endif *(.text.startup) _einittext = .; /* --- a/xen/include/xen/linkage.h +++ b/xen/include/xen/linkage.h @@ -18,6 +18,14 @@ #define SYM_ALIGN(align...) .balign align +#if defined(HAVE_AS_SECTNAME_SUBST) && defined(CONFIG_CC_SPLIT_SECTIONS) +# define SYM_PUSH_SECTION(name, attr) \ + .pushsection %S.name, attr, %progbits; \ + .equ .Lsplit_section, 1 +#else +# define SYM_PUSH_SECTION(name, attr) +#endif + #define SYM_L_GLOBAL(name) .globl name; .hidden name #define SYM_L_WEAK(name) .weak name #define SYM_L_LOCAL(name) /* nothing */ @@ -32,7 +40,14 @@ SYM_ALIGN(align); \ name: -#define END(name) .size name, . - name +#define END(name) \ + .size name, . - name; \ + .ifdef .Lsplit_section; \ + .if .Lsplit_section; \ + .popsection; \ + .equ .Lsplit_section, 0; \ + .endif; \ + .endif /* * CODE_FILL in particular may need to expand to nothing (e.g. for RISC-V), in @@ -47,6 +62,7 @@ #endif #define FUNC(name, align...) \ + SYM_PUSH_SECTION(name, "ax"); \ SYM(name, FUNC, GLOBAL, DO_CODE_ALIGN(align)) #define LABEL(name, align...) \ SYM(name, NONE, GLOBAL, DO_CODE_ALIGN(align)) @@ -54,6 +70,7 @@ SYM(name, DATA, GLOBAL, LASTARG(DATA_ALIGN, ## align), DATA_FILL) #define FUNC_LOCAL(name, align...) \ + SYM_PUSH_SECTION(name, "ax"); \ SYM(name, FUNC, LOCAL, DO_CODE_ALIGN(align)) #define LABEL_LOCAL(name, align...) \ SYM(name, NONE, LOCAL, DO_CODE_ALIGN(align))