x86/mm: Fix RESERVE_BRK() for older binutils

commit e32683c6f7d22ba624e0bfc58b02cf3348bdca63 upstream.

With binutils 2.26, RESERVE_BRK() causes a build failure:

  /tmp/ccnGOKZ5.s: Assembler messages:
  /tmp/ccnGOKZ5.s:98: Error: missing ')'
  /tmp/ccnGOKZ5.s:98: Error: missing ')'
  /tmp/ccnGOKZ5.s:98: Error: missing ')'
  /tmp/ccnGOKZ5.s:98: Error: junk at end of line, first unrecognized
  character is `U'

The problem is this line:

  RESERVE_BRK(early_pgt_alloc, INIT_PGT_BUF_SIZE)

Specifically, the INIT_PGT_BUF_SIZE macro which (via PAGE_SIZE's use
_AC()) has a "1UL", which makes older versions of the assembler unhappy.
Unfortunately the _AC() macro doesn't work for inline asm.

Inline asm was only needed here to convince the toolchain to add the
STT_NOBITS flag.  However, if a C variable is placed in a section whose
name is prefixed with ".bss", GCC and Clang automatically set
STT_NOBITS.  In fact, ".bss..page_aligned" already relies on this trick.

So fix the build failure (and simplify the macro) by allocating the
variable in C.

Also, add NOLOAD to the ".brk" output section clause in the linker
script.  This is a failsafe in case the ".bss" prefix magic trick ever
stops working somehow.  If there's a section type mismatch, the GNU
linker will force the ".brk" output section to be STT_NOBITS.  The LLVM
linker will fail with a "section type mismatch" error.

Note this also changes the name of the variable from .brk.##name to
__brk_##name.  The variable names aren't actually used anywhere, so it's
harmless.

Fixes: a1e2c031ec39 ("x86/mm: Simplify RESERVE_BRK()")
Reported-by: Joe Damato <jdamato@fastly.com>
Reported-by: Byungchul Park <byungchul.park@lge.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Joe Damato <jdamato@fastly.com>
Link: https://lore.kernel.org/r/22d07a44c80d8e8e1e82b9a806ddc8c6bbb2606e.1654759036.git.jpoimboe@kernel.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h
index c0932449cbe9c921666ec65c4c2c574a6e811136..e43ccc62fc1c35c1b32b6f8c3cd7cafd3b11707d 100644 (file)
--- a/arch/x86/include/asm/setup.h
+++ b/arch/x86/include/asm/setup.h
@@ -108,19 +108,16 @@ extern unsigned long _brk_end;
 void *extend_brk(size_t size, size_t align);
 
 /*
- * Reserve space in the brk section.  The name must be unique within the file,
- * and somewhat descriptive.  The size is in bytes.
+ * Reserve space in the .brk section, which is a block of memory from which the
+ * caller is allowed to allocate very early (before even memblock is available)
+ * by calling extend_brk().  All allocated memory will be eventually converted
+ * to memblock.  Any leftover unallocated memory will be freed.
  *
- * The allocation is done using inline asm (rather than using a section
- * attribute on a normal variable) in order to allow the use of @nobits, so
- * that it doesn't take up any space in the vmlinux file.
+ * The size is in bytes.
  */
-#define RESERVE_BRK(name, size)                                                \
-       asm(".pushsection .brk_reservation,\"aw\",@nobits\n\t"          \
-           ".brk." #name ":\n\t"                                       \
-           ".skip " __stringify(size) "\n\t"                           \
-           ".size .brk." #name ", " __stringify(size) "\n\t"           \
-           ".popsection\n\t")
+#define RESERVE_BRK(name, size)                                        \
+       __section(".bss..brk") __aligned(1) __used      \
+       static char __brk_##name[size]
 
 extern void probe_roms(void);
 #ifdef __i386__
@@ -133,12 +130,19 @@ asmlinkage void __init x86_64_start_reservations(char *real_mode_data);
 
 #endif /* __i386__ */
 #endif /* _SETUP */
-#else
-#define RESERVE_BRK(name,sz)                           \
-       .pushsection .brk_reservation,"aw",@nobits;     \
-.brk.name:                                             \
-1:     .skip sz;                                       \
-       .size .brk.name,.-1b;                           \
+
+#else  /* __ASSEMBLY */
+
+.macro __RESERVE_BRK name, size
+       .pushsection .bss..brk, "aw"
+SYM_DATA_START(__brk_\name)
+       .skip \size
+SYM_DATA_END(__brk_\name)
        .popsection
+.endm
+
+#define RESERVE_BRK(name, size) __RESERVE_BRK name, size
+
 #endif /* __ASSEMBLY__ */
+
 #endif /* _ASM_X86_SETUP_H */

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 8e56c4de00b9c9188f08987b28440c6e9339f4a4..dcfea7b01c571a6eb33ba89f7265d580d6004b50 100644 (file)
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -66,11 +66,6 @@ RESERVE_BRK(dmi_alloc, 65536);
 #endif
 
 
-/*
- * Range of the BSS area. The size of the BSS area is determined
- * at link time, with RESERVE_BRK() facility reserving additional
- * chunks.
- */
 unsigned long _brk_start = (unsigned long)__brk_base;
 unsigned long _brk_end   = (unsigned long)__brk_base;
 

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index ca1a7595edac80d1f0f4a92b92cd28c9c06577fd..bed5475b2ee94ff0e43a6c04cc6ed6a60edf7877 100644 (file)
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -411,10 +411,10 @@ SECTIONS
        __end_of_kernel_reserve = .;
 
        . = ALIGN(PAGE_SIZE);
-       .brk : AT(ADDR(.brk) - LOAD_OFFSET) {
+       .brk (NOLOAD) : AT(ADDR(.brk) - LOAD_OFFSET) {
                __brk_base = .;
                . += 64 * 1024;         /* 64k alignment slop space */
-               *(.brk_reservation)     /* areas brk users have reserved */
+               *(.bss..brk)            /* areas brk users have reserved */
                __brk_limit = .;
        }