From 7e61560628d17ea6b1d8ee370f6d42694cff8758 Mon Sep 17 00:00:00 2001 From: Ulises Mendez Martinez Date: Fri, 4 Sep 2026 15:07:09 +0000 Subject: objtool: Validate disassembler headers in libopcodes probe commit 3f2de814c059 ("objtool: Fix libopcodes linking with static libraries") tested for libopcodes availability by linking a test snippet with a forward declaration of disassemble_init_for_target(). However, testing symbol linkage with an extern declaration only verifies the presence of the library (.so/.a) and bypasses checking for development headers (binutils-dev). On systems where libopcodes is present without development headers installed, the probe succeeds, enabling BUILD_DISAS. Subsequent compilation of objtool then fails: fatal error: 'bfd.h' file not found 113 | #include Additionally, the probe invokes $(HOSTCC) without $(HOSTCFLAGS), ignoring any sysroot or include flags specified for the host compiler. Fix this by including and directly in the test snippet, passing $(HOSTCFLAGS) so host compiler options are respected, and defining PACKAGE="objtool" to satisfy the configuration check in . Fixes: 3f2de814c059 ("objtool: Fix libopcodes linking with static libraries") Fixes: 436326bc525d ("objtool: fix build failure due to missing libopcodes check") Reported-by: Alice Ryhl Assisted-by: Antigravity:Gemini-Next Signed-off-by: Ulises Mendez Martinez Link: https://patch.msgid.link/20260904150710.2997558-1-umendez@google.com Signed-off-by: Josh Poimboeuf --- lib/math/gcd.c | 88 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 88 insertions(+) create mode 100644 lib/math/gcd.c (limited to 'lib/math/gcd.c') diff --git a/lib/math/gcd.c b/lib/math/gcd.c new file mode 100644 index 000000000..62efca678 --- /dev/null +++ b/lib/math/gcd.c @@ -0,0 +1,88 @@ +// SPDX-License-Identifier: GPL-2.0-only +#include +#include +#include + +/* + * This implements the binary GCD algorithm. (Often attributed to Stein, + * but as Knuth has noted, appears in a first-century Chinese math text.) + * + * This is faster than the division-based algorithm even on x86, which + * has decent hardware division. + */ + +DEFINE_STATIC_KEY_TRUE(efficient_ffs_key); + +#if !defined(CONFIG_CPU_NO_EFFICIENT_FFS) + +/* If __ffs is available, the even/odd algorithm benchmarks slower. */ + +static unsigned long binary_gcd(unsigned long a, unsigned long b) +{ + unsigned long r = a | b; + + b >>= __ffs(b); + if (b == 1) + return r & -r; + + for (;;) { + a >>= __ffs(a); + if (a == 1) + return r & -r; + if (a == b) + return a << __ffs(r); + + if (a < b) + swap(a, b); + a -= b; + } +} + +#endif + +/* If normalization is done by loops, the even/odd algorithm is a win. */ + +/** + * gcd - calculate and return the greatest common divisor of 2 unsigned longs + * @a: first value + * @b: second value + */ +unsigned long gcd(unsigned long a, unsigned long b) +{ + unsigned long r = a | b; + + if (!a || !b) + return r; + +#if !defined(CONFIG_CPU_NO_EFFICIENT_FFS) + if (static_branch_likely(&efficient_ffs_key)) + return binary_gcd(a, b); +#endif + + /* Isolate lsbit of r */ + r &= -r; + + while (!(b & r)) + b >>= 1; + if (b == r) + return r; + + for (;;) { + while (!(a & r)) + a >>= 1; + if (a == r) + return r; + if (a == b) + return a; + + if (a < b) + swap(a, b); + a -= b; + a >>= 1; + if (a & r) + a += b; + a >>= 1; + } +} + +EXPORT_SYMBOL_GPL(gcd); -- cgit v1.3.1