kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 188 insertions, 0 deletions

diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c
new file mode 100644
index 000000000..b2813ff13
--- /dev/null
+++ b/fs/proc/meminfo.c
@@ -0,0 +1,188 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/hugetlb.h>
+#include <linux/mman.h>
+#include <linux/mmzone.h>
+#include <linux/memblock.h>
+#include <linux/proc_fs.h>
+#include <linux/percpu.h>
+#include <linux/seq_file.h>
+#include <linux/swap.h>
+#include <linux/vmstat.h>
+#include <linux/atomic.h>
+#include <linux/vmalloc.h>
+#ifdef CONFIG_CMA
+#include <linux/cma.h>
+#endif
+#include <linux/zswap.h>
+#include <asm/page.h>
+#include "internal.h"
+
+void __attribute__((weak)) arch_report_meminfo(struct seq_file *m)
+{
+}
+
+static void show_val_kb(struct seq_file *m, const char *s, unsigned long num)
+{
+	seq_put_decimal_ull_width(m, s, num << (PAGE_SHIFT - 10), 8);
+	seq_write(m, " kB\n", 4);
+}
+
+static int meminfo_proc_show(struct seq_file *m, void *v)
+{
+	struct sysinfo i;
+	unsigned long committed;
+	long cached;
+	long available;
+	unsigned long pages[NR_LRU_LISTS];
+	unsigned long sreclaimable, sunreclaim;
+	int lru;
+
+	si_meminfo(&i);
+	si_swapinfo(&i);
+	committed = vm_memory_committed();
+
+	cached = global_node_page_state(NR_FILE_PAGES) -
+			total_swapcache_pages() - i.bufferram;
+	if (cached < 0)
+		cached = 0;
+
+	for (lru = LRU_BASE; lru < NR_LRU_LISTS; lru++)
+		pages[lru] = global_node_page_state(NR_LRU_BASE + lru);
+
+	available = si_mem_available();
+	sreclaimable = global_node_page_state_pages(NR_SLAB_RECLAIMABLE_B);
+	sunreclaim = global_node_page_state_pages(NR_SLAB_UNRECLAIMABLE_B);
+
+	show_val_kb(m, "MemTotal:       ", i.totalram);
+	show_val_kb(m, "MemFree:        ", i.freeram);
+	show_val_kb(m, "MemAvailable:   ", available);
+	show_val_kb(m, "Buffers:        ", i.bufferram);
+	show_val_kb(m, "Cached:         ", cached);
+	show_val_kb(m, "SwapCached:     ", total_swapcache_pages());
+	show_val_kb(m, "Active:         ", pages[LRU_ACTIVE_ANON] +
+					   pages[LRU_ACTIVE_FILE]);
+	show_val_kb(m, "Inactive:       ", pages[LRU_INACTIVE_ANON] +
+					   pages[LRU_INACTIVE_FILE]);
+	show_val_kb(m, "Active(anon):   ", pages[LRU_ACTIVE_ANON]);
+	show_val_kb(m, "Inactive(anon): ", pages[LRU_INACTIVE_ANON]);
+	show_val_kb(m, "Active(file):   ", pages[LRU_ACTIVE_FILE]);
+	show_val_kb(m, "Inactive(file): ", pages[LRU_INACTIVE_FILE]);
+	show_val_kb(m, "Unevictable:    ", pages[LRU_UNEVICTABLE]);
+	show_val_kb(m, "Mlocked:        ", global_zone_page_state(NR_MLOCK));
+
+#ifdef CONFIG_HIGHMEM
+	show_val_kb(m, "HighTotal:      ", i.totalhigh);
+	show_val_kb(m, "HighFree:       ", i.freehigh);
+	show_val_kb(m, "LowTotal:       ", i.totalram - i.totalhigh);
+	show_val_kb(m, "LowFree:        ", i.freeram - i.freehigh);
+#endif
+
+#ifndef CONFIG_MMU
+	show_val_kb(m, "MmapCopy:       ",
+		    (unsigned long)atomic_long_read(&mmap_pages_allocated));
+#endif
+
+	show_val_kb(m, "SwapTotal:      ", i.totalswap);
+	show_val_kb(m, "SwapFree:       ", i.freeswap);
+#ifdef CONFIG_ZSWAP
+	show_val_kb(m, "Zswap:          ", zswap_total_pages());
+	seq_printf(m,  "Zswapped:       %8lu kB\n",
+		   (unsigned long)atomic_long_read(&zswap_stored_pages) <<
+		   (PAGE_SHIFT - 10));
+#endif
+	show_val_kb(m, "Dirty:          ",
+		    global_node_page_state(NR_FILE_DIRTY));
+	show_val_kb(m, "Writeback:      ",
+		    global_node_page_state(NR_WRITEBACK));
+	show_val_kb(m, "AnonPages:      ",
+		    global_node_page_state(NR_ANON_MAPPED));
+	show_val_kb(m, "Mapped:         ",
+		    global_node_page_state(NR_FILE_MAPPED));
+	show_val_kb(m, "Shmem:          ", i.sharedram);
+	show_val_kb(m, "KReclaimable:   ", sreclaimable +
+		    global_node_page_state(NR_KERNEL_MISC_RECLAIMABLE));
+	show_val_kb(m, "Slab:           ", sreclaimable + sunreclaim);
+	show_val_kb(m, "SReclaimable:   ", sreclaimable);
+	show_val_kb(m, "SUnreclaim:     ", sunreclaim);
+	seq_printf(m, "KernelStack:    %8lu kB\n",
+		   global_node_page_state(NR_KERNEL_STACK_KB));
+#ifdef CONFIG_SHADOW_CALL_STACK
+	seq_printf(m, "ShadowCallStack:%8lu kB\n",
+		   global_node_page_state(NR_KERNEL_SCS_KB));
+#endif
+	show_val_kb(m, "PageTables:     ",
+		    global_node_page_state(NR_PAGETABLE));
+	show_val_kb(m, "SecPageTables:  ",
+		    global_node_page_state(NR_SECONDARY_PAGETABLE));
+
+	show_val_kb(m, "NFS_Unstable:   ", 0);
+	show_val_kb(m, "Bounce:         ", 0);
+	show_val_kb(m, "WritebackTmp:   ", 0);
+	show_val_kb(m, "CommitLimit:    ", vm_commit_limit());
+	show_val_kb(m, "Committed_AS:   ", committed);
+	seq_printf(m, "VmallocTotal:   %8lu kB\n",
+		   (unsigned long)VMALLOC_TOTAL >> 10);
+	show_val_kb(m, "VmallocUsed:    ",
+		    global_node_page_state(NR_VMALLOC));
+	show_val_kb(m, "VmallocChunk:   ", 0ul);
+	show_val_kb(m, "Percpu:         ", pcpu_nr_pages());
+
+	memtest_report_meminfo(m);
+
+#ifdef CONFIG_MEMORY_FAILURE
+	seq_printf(m, "HardwareCorrupted: %5lu kB\n",
+		   atomic_long_read(&num_poisoned_pages) << (PAGE_SHIFT - 10));
+#endif
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+	show_val_kb(m, "AnonHugePages:  ",
+		    global_node_page_state(NR_ANON_THPS));
+	show_val_kb(m, "ShmemHugePages: ",
+		    global_node_page_state(NR_SHMEM_THPS));
+	show_val_kb(m, "ShmemPmdMapped: ",
+		    global_node_page_state(NR_SHMEM_PMDMAPPED));
+	show_val_kb(m, "FileHugePages:  ",
+		    global_node_page_state(NR_FILE_THPS));
+	show_val_kb(m, "FilePmdMapped:  ",
+		    global_node_page_state(NR_FILE_PMDMAPPED));
+#endif
+
+#ifdef CONFIG_CMA
+	show_val_kb(m, "CmaTotal:       ", totalcma_pages);
+	show_val_kb(m, "CmaFree:        ",
+		    global_zone_page_state(NR_FREE_CMA_PAGES));
+#endif
+
+#ifdef CONFIG_UNACCEPTED_MEMORY
+	show_val_kb(m, "Unaccepted:     ",
+		    global_zone_page_state(NR_UNACCEPTED));
+#endif
+	show_val_kb(m, "Balloon:        ",
+		    global_node_page_state(NR_BALLOON_PAGES));
+
+	show_val_kb(m, "GPUActive:      ",
+		    global_node_page_state(NR_GPU_ACTIVE));
+
+	show_val_kb(m, "GPUReclaim:     ",
+		    global_node_page_state(NR_GPU_RECLAIM));
+
+	hugetlb_report_meminfo(m);
+
+	arch_report_meminfo(m);
+
+	return 0;
+}
+
+static int __init proc_meminfo_init(void)
+{
+	struct proc_dir_entry *pde;
+
+	pde = proc_create_single("meminfo", 0, NULL, meminfo_proc_show);
+	pde_make_permanent(pde);
+	return 0;
+}
+fs_initcall(proc_meminfo_init);