linux-kernel - [PATCH 10/10] um: Always set up AT_HWCAP and AT

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Message-Id: <20251028-uml-remove-32bit-pseudo-vdso-v1-10-e930063eff5f@weissschuh.net>
Date: Tue, 28 Oct 2025 10:15:45 +0100
From: Thomas Weißschuh <linux@...ssschuh.net>
To: Richard Weinberger <richard@....at>, 
 Anton Ivanov <anton.ivanov@...bridgegreys.com>, 
 Johannes Berg <johannes@...solutions.net>, 
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, 
 x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, 
 Kees Cook <kees@...nel.org>
Cc: linux-um@...ts.infradead.org, linux-kernel@...r.kernel.org, 
 linux-mm@...ck.org, 
 Thomas Weißschuh <linux@...ssschuh.net>
Subject: [PATCH 10/10] um: Always set up AT_HWCAP and AT_PLATFORM

Historically the code to set up AT_HWCAP and AT_PLATFORM was only built
for 32bit x86 as it was intermingled with the vDSO passthrough code.

Now that vDSO passthrough has been removed, always pass through AT_HWCAP
and AT_PLATFORM.

Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
---
 arch/um/os-Linux/Makefile  | 4 +---
 arch/um/os-Linux/elf_aux.c | 7 ++++++-
 arch/um/os-Linux/main.c    | 4 ----
 arch/x86/um/Kconfig        | 3 ---
 arch/x86/um/asm/elf.h      | 7 ++++---
 5 files changed, 11 insertions(+), 14 deletions(-)

diff --git a/arch/um/os-Linux/Makefile b/arch/um/os-Linux/Makefile
index 70c73c22f715..f8d672d570d9 100644
--- a/arch/um/os-Linux/Makefile
+++ b/arch/um/os-Linux/Makefile
@@ -6,7 +6,7 @@
 # Don't instrument UML-specific code
 KCOV_INSTRUMENT                := n
 
-obj-y = execvp.o file.o helper.o irq.o main.o mem.o process.o \
+obj-y = elf_aux.o execvp.o file.o helper.o irq.o main.o mem.o process.o \
 	registers.o sigio.o signal.o start_up.o time.o tty.o \
 	umid.o user_syms.o util.o skas/
 
@@ -14,8 +14,6 @@ CFLAGS_signal.o += -Wframe-larger-than=4096
 
 CFLAGS_main.o += -Wno-frame-larger-than
 
-obj-$(CONFIG_ARCH_REUSE_HOST_VSYSCALL_AREA) += elf_aux.o
-
 obj-$(CONFIG_SMP) += smp.o
 
 USER_OBJS := $(user-objs-y) elf_aux.o execvp.o file.o helper.o irq.o \
diff --git a/arch/um/os-Linux/elf_aux.c b/arch/um/os-Linux/elf_aux.c
index f8927a5959d8..72f416edf252 100644
--- a/arch/um/os-Linux/elf_aux.c
+++ b/arch/um/os-Linux/elf_aux.c
@@ -14,12 +14,17 @@
 #include <elf_user.h>
 #include <mem_user.h>
 #include "internal.h"
+#include <linux/swab.h>
 
+#if __BITS_PER_LONG == 64
+typedef Elf64_auxv_t elf_auxv_t;
+#else
 typedef Elf32_auxv_t elf_auxv_t;
+#endif
 
 /* These are initialized very early in boot and never changed */
 char * elf_aux_platform;
-extern long elf_aux_hwcap;
+long elf_aux_hwcap;
 
 __init void scan_elf_aux( char **envp)
 {
diff --git a/arch/um/os-Linux/main.c b/arch/um/os-Linux/main.c
index 730723106228..7e114862a723 100644
--- a/arch/um/os-Linux/main.c
+++ b/arch/um/os-Linux/main.c
@@ -21,8 +21,6 @@
 
 #define STACKSIZE (8 * 1024 * 1024)
 
-long elf_aux_hwcap;
-
 static void __init set_stklim(void)
 {
 	struct rlimit lim;
@@ -149,9 +147,7 @@ int __init main(int argc, char **argv, char **envp)
 	install_fatal_handler(SIGINT);
 	install_fatal_handler(SIGTERM);
 
-#ifdef CONFIG_ARCH_REUSE_HOST_VSYSCALL_AREA
 	scan_elf_aux(envp);
-#endif
 
 	change_sig(SIGPIPE, 0);
 	ret = linux_main(argc, argv, envp);
diff --git a/arch/x86/um/Kconfig b/arch/x86/um/Kconfig
index 798c6cc53e82..bdd7c8e39b01 100644
--- a/arch/x86/um/Kconfig
+++ b/arch/x86/um/Kconfig
@@ -34,8 +34,5 @@ config X86_64
 config ARCH_HAS_SC_SIGNALS
 	def_bool !64BIT
 
-config ARCH_REUSE_HOST_VSYSCALL_AREA
-	def_bool !64BIT
-
 config GENERIC_HWEIGHT
 	def_bool y
diff --git a/arch/x86/um/asm/elf.h b/arch/x86/um/asm/elf.h
index fdd5a612f678..22d0111b543b 100644
--- a/arch/x86/um/asm/elf.h
+++ b/arch/x86/um/asm/elf.h
@@ -68,9 +68,7 @@
 	pr_reg[16] = PT_REGS_SS(regs);		\
 } while (0);
 
-extern char * elf_aux_platform;
 #define ELF_PLATFORM_FALLBACK "i586"
-#define ELF_PLATFORM (elf_aux_platform ?: ELF_PLATFORM_FALLBACK)
 
 #else
 
@@ -151,7 +149,7 @@ extern char * elf_aux_platform;
 	(pr_reg)[25] = 0;					\
 	(pr_reg)[26] = 0;
 
-#define ELF_PLATFORM "x86_64"
+#define ELF_PLATFORM_FALLBACK "x86_64"
 
 #define ARCH_HAS_SETUP_ADDITIONAL_PAGES 1
 struct linux_binprm;
@@ -180,6 +178,9 @@ struct task_struct;
 extern long elf_aux_hwcap;
 #define ELF_HWCAP (elf_aux_hwcap)
 
+extern char *elf_aux_platform;
+#define ELF_PLATFORM (elf_aux_platform ?: ELF_PLATFORM_FALLBACK)
+
 #define SET_PERSONALITY(ex) do {} while(0)
 
 #endif

-- 
2.51.1.dirty