Attachment 248228 Details for Bug 247327 – comment cleanup (v2)

[patch] comment cleanup (v2)

0001-linux-4-use-GUFS32_SEL-for-the-second-GDT-descriptor.patch (text/plain), 4.44 KB, created by Alex S on 2024-02-07 13:17:20 UTC

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Creator: Alex S

Created: 2024-02-07 13:17:20 UTC

Size: 4.44 KB

patch

obsolete

>From 024df21168b5baaecfd2b1e36887fce9c6388136 Mon Sep 17 00:00:00 2001
>From: Alex S <iwtcex@gmail.com>
>Date: Sun, 4 Feb 2024 03:09:03 +0300
>Subject: [PATCH] linux(4): use GUFS32_SEL for the second GDT descriptor in
> linux_set_thread_area
>
>We maintain 2 descriptor entries that are suitable for TLS on AMD64,
>not just one. This partially unbreaks i386 Wine.
>---
> sys/amd64/linux32/linux32_machdep.c | 74 +++++++++++++----------------
> sys/compat/linux/linux_emul.c       |  1 +
> sys/compat/linux/linux_emul.h       |  2 +
> 3 files changed, 37 insertions(+), 40 deletions(-)
>
>diff --git a/sys/amd64/linux32/linux32_machdep.c b/sys/amd64/linux32/linux32_machdep.c
>index 9746c4bd7..83eea1b8e 100644
>--- a/sys/amd64/linux32/linux32_machdep.c
>+++ b/sys/amd64/linux32/linux32_machdep.c
>@@ -628,6 +628,7 @@ linux_set_thread_area(struct thread *td,
>     struct linux_set_thread_area_args *args)
> {
> 	struct l_user_desc info;
>+	struct linux_emuldata *em;
> 	struct pcb *pcb;
> 	int error;
> 
>@@ -635,55 +636,48 @@ linux_set_thread_area(struct thread *td,
> 	if (error)
> 		return (error);
> 
>-	/*
>-	 * Semantics of Linux version: every thread in the system has array
>-	 * of three TLS descriptors. 1st is GLIBC TLS, 2nd is WINE, 3rd unknown.
>-	 * This syscall loads one of the selected TLS decriptors with a value
>-	 * and also loads GDT descriptors 6, 7 and 8 with the content of
>-	 * the per-thread descriptors.
>-	 *
>-	 * Semantics of FreeBSD version: I think we can ignore that Linux has
>-	 * three per-thread descriptors and use just the first one.
>-	 * The tls_array[] is used only in [gs]et_thread_area() syscalls and
>-	 * for loading the GDT descriptors. We use just one GDT descriptor
>-	 * for TLS, so we will load just one.
>-	 *
>-	 * XXX: This doesn't work when a user space process tries to use more
>-	 * than one TLS segment. Comment in the Linux source says wine might
>-	 * do this.
>+	/* Linux keeps 3 GDT entries for TLS: glibc uses the first one,
>+	 * Wine uses the second and nobody seems to be using the third.
>+	 * We only maintain 2 such entries, so that suits us just fine.
> 	 */
>+	if (info.entry_number == -1) {
>+		em = em_find(td);
>+		switch (em->tls_slots_used) {
>+		case 0:
>+			info.entry_number = GUGS32_SEL;
>+			em->tls_slots_used++;
>+			break;
>+		case 1:
>+			info.entry_number = GUFS32_SEL;
>+			em->tls_slots_used++;
>+			break;
>+		default:
>+			return (ESRCH);
>+		}
>+
>+		/* We have to copy out entry_number. */
>+		error = copyout(&info, args->desc, sizeof(struct l_user_desc));
>+		if (error)
>+			return (error);
>+	}
> 
>-	/*
>-	 * GLIBC reads current %gs and call set_thread_area() with it.
>-	 * We should let GUDATA_SEL and GUGS32_SEL proceed as well because
>-	 * we use these segments.
>-	 */
> 	switch (info.entry_number) {
> 	case GUGS32_SEL:
>-	case GUDATA_SEL:
>-	case 6:
>-	case -1:
>-		info.entry_number = GUGS32_SEL;
>+		pcb = td->td_pcb;
>+		update_pcb_bases(pcb);
>+		pcb->pcb_gsbase = (register_t)info.base_addr;
>+		update_gdt_gsbase(td, info.base_addr);
>+		break;
>+	case GUFS32_SEL:
>+		pcb = td->td_pcb;
>+		update_pcb_bases(pcb);
>+		pcb->pcb_fsbase = (register_t)info.base_addr;
>+		update_gdt_fsbase(td, info.base_addr);
> 		break;
> 	default:
> 		return (EINVAL);
> 	}
> 
>-	/*
>-	 * We have to copy out the GDT entry we use.
>-	 *
>-	 * XXX: What if a user space program does not check the return value
>-	 * and tries to use 6, 7 or 8?
>-	 */
>-	error = copyout(&info, args->desc, sizeof(struct l_user_desc));
>-	if (error)
>-		return (error);
>-
>-	pcb = td->td_pcb;
>-	update_pcb_bases(pcb);
>-	pcb->pcb_gsbase = (register_t)info.base_addr;
>-	update_gdt_gsbase(td, info.base_addr);
>-
> 	return (0);
> }
> 
>diff --git a/sys/compat/linux/linux_emul.c b/sys/compat/linux/linux_emul.c
>index 08510fc29..511e0535c 100644
>--- a/sys/compat/linux/linux_emul.c
>+++ b/sys/compat/linux/linux_emul.c
>@@ -183,6 +183,7 @@ linux_proc_init(struct thread *td, struct thread *newtd, bool init_thread)
> 		em->robust_futexes = NULL;
> 		em->child_clear_tid = NULL;
> 		em->child_set_tid = NULL;
>+		em->tls_slots_used = 0;
> 
> 		pem = pem_find(p);
> 		KASSERT(pem != NULL, ("proc_init: proc emuldata not found.\n"));
>diff --git a/sys/compat/linux/linux_emul.h b/sys/compat/linux/linux_emul.h
>index fde97c018..0b2b8c71e 100644
>--- a/sys/compat/linux/linux_emul.h
>+++ b/sys/compat/linux/linux_emul.h
>@@ -46,6 +46,8 @@ struct linux_emuldata {
> 	int	em_tid;			/* thread id */
> 
> 	struct	linux_robust_list_head	*robust_futexes;
>+
>+	int tls_slots_used; /* GDT descriptor count for set_thread_area() on i386/amd64 */
> };
> 
> struct linux_emuldata	*em_find(struct thread *);
>-- 
>2.42.0
>

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Attachments on bug 247327: 248191 | 248228 | 248297 | 248298 | 248299