[PATCH 1/3] x86/purgatory: Compile purgatory with -D__NO_FORTIFY and -D__DISABLE_EXPORTS

[Thomas Huth <thuth@redhat.com>]

A subsequent patch will add #include <linux/string.h> to <crypto/sha2.h>
to use memzero_explicit() there. This will introduce a conflict with the
purgatory code: purgatory.c includes both, the <crypto/sha2.h> header and
the arch/x86/boot/string.h header. The latter provides its own prototypes
for a lot of string functions which clash with the fortified macros
from <linux/string.h>, causing the compiler to emit errors like this:

 In file included from .../linux/include/linux/string.h:383,
                  from .../linux/include/crypto/sha2.h:10,
                  from .../linux/arch/x86/purgatory/purgatory.c:14:
 .../linux/include/linux/fortify-string.h:576:63: error: expected identifier or ‘(’ before ‘{’ token
   576 |                              p_size_field, q_size_field, op) ({         \
       |                                                               ^
 .../linux/include/linux/fortify-string.h:644:27: note: in expansion of macro ‘__fortify_memcpy_chk’
   644 | #define memmove(p, q, s)  __fortify_memcpy_chk(p, q, s,                 \
       |                           ^~~~~~~~~~~~~~~~~~~~
 .../linux/arch/x86/purgatory/../boot/string.h:11:7: note: in expansion of macro ‘memmove’
    11 | void *memmove(void *dst, const void *src, size_t len);
       |       ^~~~~~~
 .../linux/include/linux/fortify-string.h:208:9: error: expected identifier or ‘(’ before ‘__builtin_choose_expr’
   208 |         __builtin_choose_expr(__is_constexpr(__builtin_strlen(p)),      \
       |         ^~~~~~~~~~~~~~~~~~~~~
 ./linux/arch/x86/purgatory/../boot/string.h:23:15: note: in expansion of macro ‘strlen’
    23 | extern size_t strlen(const char *s);
       |               ^~~~~~

To avoid the problem, let's compile the whole code in the purgatory with
-D__NO_FORTIFY, so <linux/string.h> can properly be included from headers
like <crypto/sha2.h> in the purgatory, too.

When compiling/linking with the LLVM tools, and CONFIG_CFI=y, there is
an additional problem during linking:

 ld.lld: error: undefined symbol: __memset
 >>> referenced by string.c
 >>>               arch/x86/purgatory/purgatory.ro:(__UNIQUE_ID_addressable___memset_5)
 ld.lld: error: undefined symbol: __memmove
 >>> referenced by string.c
 >>>               arch/x86/purgatory/purgatory.ro:(__UNIQUE_ID_addressable___memmove_6)

This can be fixed by moving the -D__DISABLE_EXPORTS to the general CFLAGS
of the purgatory, too.

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 arch/x86/purgatory/Makefile | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
index 5ce1d42630000..fad91ea28fe71 100644
--- a/arch/x86/purgatory/Makefile
+++ b/arch/x86/purgatory/Makefile
@@ -11,8 +11,6 @@ $(obj)/string.o: $(srctree)/arch/x86/boot/compressed/string.c FORCE
 $(obj)/sha256.o: $(srctree)/lib/crypto/sha256.c FORCE
 	$(call if_changed_rule,cc_o_c)
 
-CFLAGS_sha256.o := -D__DISABLE_EXPORTS -D__NO_FORTIFY
-
 # When profile-guided optimization is enabled, llvm emits two different
 # overlapping text sections, which is not supported by kexec. Remove profile
 # optimization flags.
@@ -37,6 +35,7 @@ PURGATORY_CFLAGS := -mcmodel=small -ffreestanding -fno-zero-initialized-in-bss -
 PURGATORY_CFLAGS += -fpic -fvisibility=hidden
 PURGATORY_CFLAGS += $(DISABLE_KSTACK_ERASE) -DDISABLE_BRANCH_PROFILING
 PURGATORY_CFLAGS += -fno-stack-protector
+PURGATORY_CFLAGS += -D__DISABLE_EXPORTS -D__NO_FORTIFY
 
 # Default KBUILD_CFLAGS can have -pg option set when FTRACE is enabled. That
 # in turn leaves some undefined symbols like __fentry__ in purgatory and not
-- 
2.55.0