linux-user/arm: Add vdso

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

linux-user/arm/Makefile.vdso

@@ -0,0 +1,17 @@
+include $(BUILD_DIR)/tests/tcg/arm-linux-user/config-target.mak
+
+SUBDIR = $(SRC_PATH)/linux-user/arm
+VPATH += $(SUBDIR)
+
+all: $(SUBDIR)/vdso-be.so $(SUBDIR)/vdso-le.so
+
+# Adding -use-blx disables unneeded interworking without actually using blx.
+LDFLAGS = -nostdlib -shared -Wl,-use-blx \
+	  -Wl,-h,linux-vdso.so.1 -Wl,--build-id=sha1 \
+	  -Wl,--hash-style=both -Wl,-T,$(SUBDIR)/vdso.ld
+
+$(SUBDIR)/vdso-be.so: vdso.S vdso.ld vdso-asmoffset.h
+	$(CC) -o $@ $(LDFLAGS) -mbig-endian $<
+
+$(SUBDIR)/vdso-le.so: vdso.S vdso.ld vdso-asmoffset.h
+	$(CC) -o $@ $(LDFLAGS) -mlittle-endian $<

linux-user/arm/meson.build

@@ -5,3 +5,15 @@ syscall_nr_generators += {
                    arguments: [ meson.current_source_dir() / 'syscallhdr.sh', '@INPUT@', '@OUTPUT@', '@EXTRA_ARGS@' ],
                    output: '@BASENAME@_nr.h')
 }
+
+# TARGET_BIG_ENDIAN is defined to 'n' for little-endian; which means it
+# is always true as far as source_set.apply() is concerned.  Always build
+# both header files and include the right one via #if.
+
+vdso_be_inc = gen_vdso.process('vdso-be.so',
+                               extra_args: ['-s', 'sigreturn_codes'])
+
+vdso_le_inc = gen_vdso.process('vdso-le.so',
+                               extra_args: ['-s', 'sigreturn_codes'])
+
+linux_user_ss.add(when: 'TARGET_ARM', if_true: [vdso_be_inc, vdso_le_inc])

linux-user/arm/signal.c

@@ -21,6 +21,7 @@
 #include "user-internals.h"
 #include "signal-common.h"
 #include "linux-user/trace.h"
+#include "vdso-asmoffset.h"
 
 struct target_sigcontext {
     abi_ulong trap_no;
@@ -102,6 +103,11 @@ struct rt_sigframe
     struct sigframe sig;
 };
 
+QEMU_BUILD_BUG_ON(offsetof(struct sigframe, retcode[3])
+                  != SIGFRAME_RC3_OFFSET);
+QEMU_BUILD_BUG_ON(offsetof(struct rt_sigframe, sig.retcode[3])
+                  != RT_SIGFRAME_RC3_OFFSET);
+
 static abi_ptr sigreturn_fdpic_tramp;
 
 /*
@@ -160,6 +166,9 @@ get_sigframe(struct target_sigaction *ka, CPUARMState *regs, int framesize)
     return (sp - framesize) & ~7;
 }
 
+static void write_arm_sigreturn(uint32_t *rc, int syscall);
+static void write_arm_fdpic_sigreturn(uint32_t *rc, int ofs);
+
 static int
 setup_return(CPUARMState *env, struct target_sigaction *ka, int usig,
              struct sigframe *frame, abi_ulong sp_addr)
@@ -167,9 +176,9 @@ setup_return(CPUARMState *env, struct target_sigaction *ka, int usig,
     abi_ulong handler = 0;
     abi_ulong handler_fdpic_GOT = 0;
     abi_ulong retcode;
-    int thumb, retcode_idx;
-    int is_fdpic = info_is_fdpic(((TaskState *)thread_cpu->opaque)->info);
-    bool copy_retcode;
+    bool is_fdpic = info_is_fdpic(((TaskState *)thread_cpu->opaque)->info);
+    bool is_rt = ka->sa_flags & TARGET_SA_SIGINFO;
+    bool thumb;
 
     if (is_fdpic) {
         /* In FDPIC mode, ka->_sa_handler points to a function
@@ -184,9 +193,7 @@ setup_return(CPUARMState *env, struct target_sigaction *ka, int usig,
     } else {
         handler = ka->_sa_handler;
     }
-
     thumb = handler & 1;
-    retcode_idx = thumb + (ka->sa_flags & TARGET_SA_SIGINFO ? 2 : 0);
 
     uint32_t cpsr = cpsr_read(env);
 
@@ -202,24 +209,32 @@ setup_return(CPUARMState *env, struct target_sigaction *ka, int usig,
         cpsr &= ~CPSR_E;
     }
 
+    /* Our vdso default_sigreturn label is a table of entry points. */
+    retcode = default_sigreturn + (is_fdpic * 2 + is_rt) * 8;
+
+    /*
+     * Put the sigreturn code on the stack no matter which return
+     * mechanism we use in order to remain ABI compliant.
+     * Because this is about ABI, always use the A32 instructions,
+     * despite the fact that our actual vdso trampoline is T16.
+     */
+    if (is_fdpic) {
+        write_arm_fdpic_sigreturn(frame->retcode,
+                                  is_rt ? RT_SIGFRAME_RC3_OFFSET
+                                        : SIGFRAME_RC3_OFFSET);
+    } else {
+        write_arm_sigreturn(frame->retcode,
+                            is_rt ? TARGET_NR_rt_sigreturn
+                                  : TARGET_NR_sigreturn);
+    }
+
     if (ka->sa_flags & TARGET_SA_RESTORER) {
         if (is_fdpic) {
+            /* Place the function descriptor in slot 3. */
             __put_user((abi_ulong)ka->sa_restorer, &frame->retcode[3]);
-            retcode = (sigreturn_fdpic_tramp +
-                       retcode_idx * RETCODE_BYTES + thumb);
-            copy_retcode = true;
         } else {
             retcode = ka->sa_restorer;
-            copy_retcode = false;
         }
-    } else {
-        retcode = default_sigreturn + retcode_idx * RETCODE_BYTES + thumb;
-        copy_retcode = true;
-    }
-
-    /* Copy the code to the stack slot for ABI compatibility. */
-    if (copy_retcode) {
-        memcpy(frame->retcode, g2h_untagged(retcode & ~1), RETCODE_BYTES);
     }
 
     env->regs[0] = usig;

linux-user/arm/vdso-asmoffset.h

@@ -0,0 +1,3 @@
+/* offsetof(struct sigframe, retcode[3]) */
+#define SIGFRAME_RC3_OFFSET     756
+#define RT_SIGFRAME_RC3_OFFSET  884

linux-user/arm/vdso.S

@@ -0,0 +1,174 @@
+/*
+ * arm linux replacement vdso.
+ *
+ * Copyright 2023 Linaro, Ltd.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include <asm/unistd.h>
+#include "vdso-asmoffset.h"
+
+/*
+ * All supported cpus have T16 instructions: at least arm4t.
+ *
+ * We support user-user with m-profile cpus as an extension, because it
+ * is useful for testing gcc, which requires we avoid A32 instructions.
+ */
+	.thumb
+	.arch	armv4t
+	.eabi_attribute Tag_FP_arch, 0
+	.eabi_attribute Tag_ARM_ISA_use, 0
+
+	.text
+
+.macro	raw_syscall n
+	.ifne \n < 0x100
+	mov	r7, #\n
+	.elseif \n < 0x1ff
+	mov	r7, #0xff
+	add	r7, #(\n - 0xff)
+	.else
+	.err
+	.endif
+	swi	#0
+.endm
+
+.macro	fdpic_thunk ofs
+	ldr	r3, [sp, #\ofs]
+	ldmia	r2, {r2, r3}
+	mov	r9, r3
+	bx	r2
+.endm
+
+.macro	endf name
+	.globl	\name
+	.type	\name, %function
+	.size	\name, . - \name
+.endm
+
+/*
+ * We must save/restore r7 for the EABI syscall number.
+ * While we're doing that, we might as well save LR to get a free return,
+ * and a branch that is interworking back to ARMv5.
+ */
+
+.macro SYSCALL name, nr
+\name:
+	.cfi_startproc
+	push	{r7, lr}
+	.cfi_adjust_cfa_offset 8
+	.cfi_offset r7, -8
+	.cfi_offset lr, -4
+	raw_syscall \nr
+	pop	{r7, pc}
+	.cfi_endproc
+endf \name
+.endm
+
+SYSCALL	__vdso_clock_gettime, __NR_clock_gettime
+SYSCALL __vdso_clock_gettime64, __NR_clock_gettime64
+SYSCALL __vdso_clock_getres, __NR_clock_getres
+SYSCALL __vdso_gettimeofday, __NR_gettimeofday
+
+
+/*
+ * We, like the real kernel, use a table of sigreturn trampolines.
+ * Unlike the real kernel, we do not attempt to pack this into as
+ * few bytes as possible -- simply use 8 bytes per slot.
+ *
+ * Within each slot, use the exact same code sequence as the kernel,
+ * lest we trip up someone doing code inspection.
+ */
+
+.macro	slot n
+	.balign	8
+	.org	sigreturn_codes + 8 * \n
+.endm
+
+.macro cfi_fdpic_r9 ofs
+	/*
+	 * fd = *(r13 + ofs)
+         * r9 = *(fd + 4)
+	 *
+	 * DW_CFA_expression r9, length (7),
+	 *   DW_OP_breg13, ofs, DW_OP_deref,
+	 *   DW_OP_plus_uconst, 4, DW_OP_deref
+         */
+	.cfi_escape 0x10, 9, 7, 0x7d, (\ofs & 0x7f) + 0x80, (\ofs >> 7), 0x06, 0x23, 4, 0x06
+.endm
+
+.macro cfi_fdpic_pc ofs
+	/*
+	 * fd = *(r13 + ofs)
+         * pc = *fd
+	 *
+	 * DW_CFA_expression lr (14), length (5),
+	 *   DW_OP_breg13, ofs, DW_OP_deref, DW_OP_deref
+         */
+	.cfi_escape 0x10, 14, 5, 0x7d, (\ofs & 0x7f) + 0x80, (\ofs >> 7), 0x06, 0x06
+.endm
+
+/*
+ * Start the unwind info at least one instruction before the signal
+ * trampoline, because the unwinder will assume we are returning
+ * after a call site.
+ */
+	.cfi_startproc simple
+	.cfi_signal_frame
+	.cfi_return_column 15
+
+	.cfi_def_cfa	sp, 32 + 64
+	.cfi_offset	r0, -16 * 4
+	.cfi_offset	r1, -15 * 4
+	.cfi_offset	r2, -14 * 4
+	.cfi_offset	r3, -13 * 4
+	.cfi_offset	r4, -12 * 4
+	.cfi_offset	r5, -11 * 4
+	.cfi_offset	r6, -10 * 4
+	.cfi_offset	r7, -9 * 4
+	.cfi_offset	r8, -8 * 4
+	.cfi_offset	r9, -7 * 4
+	.cfi_offset	r10, -6 * 4
+	.cfi_offset	r11, -5 * 4
+	.cfi_offset	r12, -4 * 4
+	.cfi_offset	r13, -3 * 4
+	.cfi_offset	r14, -2 * 4
+	.cfi_offset	r15, -1 * 4
+
+	nop
+
+	.balign	16
+sigreturn_codes:
+	/* [EO]ABI sigreturn */
+	slot	0
+	raw_syscall __NR_sigreturn
+
+	.cfi_def_cfa_offset 160 + 64
+
+	/* [EO]ABI rt_sigreturn */
+	slot	1
+	raw_syscall __NR_rt_sigreturn
+
+	.cfi_endproc
+
+	/* FDPIC sigreturn */
+	.cfi_startproc
+	cfi_fdpic_pc SIGFRAME_RC3_OFFSET
+	cfi_fdpic_r9 SIGFRAME_RC3_OFFSET
+
+	slot	2
+	fdpic_thunk SIGFRAME_RC3_OFFSET
+	.cfi_endproc
+
+	/* FDPIC rt_sigreturn */
+	.cfi_startproc
+	cfi_fdpic_pc RT_SIGFRAME_RC3_OFFSET
+	cfi_fdpic_r9 RT_SIGFRAME_RC3_OFFSET
+
+	slot	3
+	fdpic_thunk RT_SIGFRAME_RC3_OFFSET
+	.cfi_endproc
+
+	.balign	16
+endf sigreturn_codes

linux-user/arm/vdso.ld

@@ -0,0 +1,67 @@
+/*
+ * Linker script for linux arm replacement vdso.
+ *
+ * Copyright 2023 Linaro, Ltd.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+VERSION {
+        LINUX_2.6 {
+        global:
+                __vdso_clock_gettime;
+                __vdso_gettimeofday;
+                __vdso_clock_getres;
+                __vdso_clock_gettime64;
+
+        local: *;
+        };
+}
+
+
+PHDRS {
+        phdr            PT_PHDR         FLAGS(4) PHDRS;
+        load            PT_LOAD         FLAGS(7) FILEHDR PHDRS; /* FLAGS=RWX */
+        dynamic         PT_DYNAMIC      FLAGS(4);
+        eh_frame_hdr    PT_GNU_EH_FRAME;
+        note            PT_NOTE         FLAGS(4);
+}
+
+SECTIONS {
+        . = SIZEOF_HEADERS;
+
+        /*
+         * The following, including the FILEHDRS and PHDRS, are modified
+         * when we relocate the binary.  We want them to be initially
+         * writable for the relocation; we'll force them read-only after.
+         */
+        .note           : { *(.note*) }         :load :note
+        .dynamic        : { *(.dynamic) }       :load :dynamic
+        .dynsym         : { *(.dynsym) }        :load
+        /*
+         * There ought not be any real read-write data.
+         * But since we manipulated the segment layout,
+         * we have to put these sections somewhere.
+         */
+        .data           : {
+                *(.data*)
+                *(.sdata*)
+                *(.got.plt) *(.got)
+                *(.gnu.linkonce.d.*)
+                *(.bss*)
+                *(.dynbss*)
+                *(.gnu.linkonce.b.*)
+        }
+
+        .rodata         : { *(.rodata*) }
+        .hash           : { *(.hash) }
+        .gnu.hash       : { *(.gnu.hash) }
+        .dynstr         : { *(.dynstr) }
+        .gnu.version    : { *(.gnu.version) }
+        .gnu.version_d  : { *(.gnu.version_d) }
+        .gnu.version_r  : { *(.gnu.version_r) }
+        .eh_frame_hdr   : { *(.eh_frame_hdr) }  :load :eh_frame_hdr
+        .eh_frame       : { *(.eh_frame) }      :load
+
+        .text           : { *(.text*) }         :load
+}

linux-user/elfload.c

@@ -944,13 +944,14 @@ const char *elf_hwcap2_str(uint32_t bit)
 
 #undef GET_FEATURE_ID
 
+#endif /* not TARGET_AARCH64 */
+
 #if TARGET_BIG_ENDIAN
 # define VDSO_HEADER  "vdso-be.c.inc"
 #else
 # define VDSO_HEADER  "vdso-le.c.inc"
 #endif
 
-#endif /* not TARGET_AARCH64 */
 #endif /* TARGET_ARM */
 
 #ifdef TARGET_SPARC