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Fix global pointer relaxations in the RISC-V kernel

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The gp register is intended to used by the linker as another means of
performing relaxations, and should point to the small data section (.sdata).

Currently gp is being used as the pcpu pointer within the kernel, but the more
appropriate choice for this is the tp register, which is unused.

Swap existing usage of gp with tp within the kernel, and set up gp properly
at boot with the value of __global_pointer$ for all harts.

Additionally, remove some cases of accessing tp from the PCB, as it is not
part of the per-thread state. The user's tp and gp should be tracked only
through the trapframe.

Reviewed by:	markj, jhb
Approved by:	markj (mentor)
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D19893
This commit is contained in:
Mitchell Horne 2019-06-09 15:43:38 +00:00
parent fc261c16bd
commit 6ae48dd870
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=348836
9 changed files with 54 additions and 47 deletions
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6
sys/conf/ldscript.riscv
View File

@ -89,7 +89,11 @@ SECTIONS
can access them all, and initialized data all before uninitialized, so
we can shorten the on-disk segment size. */
. = ALIGN(8);
.sdata : { *(.sdata) }
.sdata :
{
__global_pointer$ = . + 0x800;
*(.sdata)
}
_edata = .;
PROVIDE (edata = .);
/* Ensure __bss_start is associated with the next section in case orphan

2
sys/riscv/include/asm.h
View File

@ -59,7 +59,7 @@
.set alias,sym
#define SET_FAULT_HANDLER(handler, tmp) \
ld tmp, PC_CURTHREAD(gp); \
ld tmp, PC_CURTHREAD(tp); \
ld tmp, TD_PCB(tmp); /* Load the pcb */ \
sd handler, PCB_ONFAULT(tmp) /* Set the handler */

4
sys/riscv/include/pcpu.h
View File

@ -60,7 +60,7 @@ get_pcpu(void)
{
struct pcpu *pcpu;
__asm __volatile("mv %0, gp" : "=&r"(pcpu));
__asm __volatile("mv %0, tp" : "=&r"(pcpu));
return (pcpu);
}
@ -70,7 +70,7 @@ get_curthread(void)
{
struct thread *td;
__asm __volatile("ld %0, 0(gp)" : "=&r"(td));
__asm __volatile("ld %0, 0(tp)" : "=&r"(td));
return (td);
}

23
sys/riscv/riscv/exception.S
View File

@ -44,11 +44,18 @@ __FBSDID("$FreeBSD$");
addi sp, sp, -(TF_SIZE)
sd ra, (TF_RA)(sp)
sd tp, (TF_TP)(sp)
.if \el == 0 /* We came from userspace. Load our pcpu */
.if \el == 0 /* We came from userspace. */
sd gp, (TF_GP)(sp)
ld gp, (TF_SIZE)(sp)
.option push
.option norelax
/* Load the kernel's global pointer */
la gp, __global_pointer$
.option pop
/* Load our pcpu */
sd tp, (TF_TP)(sp)
ld tp, (TF_SIZE)(sp)
.endif
sd t0, (TF_T + 0 * 8)(sp)
@ -128,13 +135,15 @@ __FBSDID("$FreeBSD$");
ld t0, (TF_SP)(sp)
csrw sscratch, t0
/* And store our pcpu */
sd gp, (TF_SIZE)(sp)
/* Store our pcpu */
sd tp, (TF_SIZE)(sp)
ld tp, (TF_TP)(sp)
/* And restore the user's global pointer */
ld gp, (TF_GP)(sp)
.endif
ld ra, (TF_RA)(sp)
ld tp, (TF_TP)(sp)
ld t0, (TF_T + 0 * 8)(sp)
ld t1, (TF_T + 1 * 8)(sp)
@ -175,7 +184,7 @@ __FBSDID("$FreeBSD$");
1:
csrci sstatus, (SSTATUS_SIE)
ld a1, PC_CURTHREAD(gp)
ld a1, PC_CURTHREAD(tp)
lw a2, TD_FLAGS(a1)
li a3, (TDF_ASTPENDING|TDF_NEEDRESCHED)

20
sys/riscv/riscv/locore.S
View File

@ -171,12 +171,18 @@ va:
li t0, 0
csrw sscratch, t0
/* Set the global pointer */
.option push
.option norelax
la gp, __global_pointer$
.option pop
/* Initialize stack pointer */
la s3, initstack_end
mv sp, s3
addi sp, sp, -PCB_SIZE
/* Clear BSS */
/* Clear BSS */
la s0, _C_LABEL(__bss_start)
la s1, _C_LABEL(_end)
1:
@ -251,12 +257,6 @@ virt_map:
hart_lottery:
.space 4
/* Not in use, but required for linking. */
.align 3
.globl __global_pointer$
__global_pointer$:
.space 8
.globl init_pt_va
init_pt_va:
.quad pagetable_l2 /* XXX: Keep page tables VA */
@ -324,6 +324,12 @@ mpva:
li t0, 0
csrw sscratch, t0
/* Set the global pointer */
.option push
.option norelax
la gp, __global_pointer$
.option pop
call init_secondary
END(mpentry)
#endif

2
sys/riscv/riscv/machdep.c
View File

@ -822,7 +822,7 @@ initriscv(struct riscv_bootparams *rvbp)
pcpup->pc_hart = boot_hart;
/* Set the pcpu pointer */
__asm __volatile("mv gp, %0" :: "r"(pcpup));
__asm __volatile("mv tp, %0" :: "r"(pcpup));
PCPU_SET(curthread, &thread0);

2
sys/riscv/riscv/mp_machdep.c
View File

@ -234,7 +234,7 @@ init_secondary(uint64_t hart)
/* Setup the pcpu pointer */
pcpup = &__pcpu[cpuid];
__asm __volatile("mv gp, %0" :: "r"(pcpup));
__asm __volatile("mv tp, %0" :: "r"(pcpup));
/* Workaround: make sure wfi doesn't halt the hart */
csr_set(sie, SIE_SSIE);

19
sys/riscv/riscv/swtch.S
View File

@ -217,15 +217,14 @@ ENTRY(cpu_throw)
mv a0, s0
/* Store the new curthread */
sd a0, PC_CURTHREAD(gp)
sd a0, PC_CURTHREAD(tp)
/* And the new pcb */
ld x13, TD_PCB(a0)
sd x13, PC_CURPCB(gp)
sd x13, PC_CURPCB(tp)
/* Load registers */
ld ra, (PCB_RA)(x13)
ld sp, (PCB_SP)(x13)
ld tp, (PCB_TP)(x13)
/* s[0-11] */
ld s0, (PCB_S + 0 * 8)(x13)
@ -267,10 +266,10 @@ END(cpu_throw)
*/
ENTRY(cpu_switch)
/* Store the new curthread */
sd a1, PC_CURTHREAD(gp)
sd a1, PC_CURTHREAD(tp)
/* And the new pcb */
ld x13, TD_PCB(a1)
sd x13, PC_CURPCB(gp)
sd x13, PC_CURPCB(tp)
/* Save the old context. */
ld x13, TD_PCB(a0)
@ -278,7 +277,6 @@ ENTRY(cpu_switch)
/* Store ra, sp and the callee-saved registers */
sd ra, (PCB_RA)(x13)
sd sp, (PCB_SP)(x13)
sd tp, (PCB_TP)(x13)
/* s[0-11] */
sd s0, (PCB_S + 0 * 8)(x13)
@ -340,7 +338,6 @@ ENTRY(cpu_switch)
ld x13, TD_PCB(a1)
/* Restore the registers */
ld tp, (PCB_TP)(x13)
ld ra, (PCB_RA)(x13)
ld sp, (PCB_SP)(x13)
@ -429,15 +426,16 @@ ENTRY(fork_trampoline)
ld a6, (TF_A + 6 * 8)(sp)
ld a7, (TF_A + 7 * 8)(sp)
/* Load user ra and sp */
/* Load user ra and gp */
ld ra, (TF_RA)(sp)
ld gp, (TF_GP)(sp)
/*
* Store our pcpup on stack, we will load it back
* on kernel mode trap.
*/
sd gp, (TF_SIZE)(sp)
ld gp, (TF_GP)(sp)
sd tp, (TF_SIZE)(sp)
ld tp, (TF_TP)(sp)
/* Save kernel stack so we can use it doing a user trap */
addi sp, sp, TF_SIZE
@ -454,6 +452,7 @@ ENTRY(savectx)
sd ra, (PCB_RA)(a0)
sd sp, (PCB_SP)(a0)
sd tp, (PCB_TP)(a0)
sd gp, (PCB_GP)(a0)
/* s[0-11] */
sd s0, (PCB_S + 0 * 8)(a0)

23
sys/riscv/riscv/vm_machdep.c
View File

@ -69,22 +69,11 @@ cpu_fork(struct thread *td1, struct proc *p2, struct thread *td2, int flags)
{
struct pcb *pcb2;
struct trapframe *tf;
register_t val;
if ((flags & RFPROC) == 0)
return;
if (td1 == curthread) {
/*
* Save the tp. These normally happen in cpu_switch,
* but if userland changes this then forks this may
* not have happened.
*/
__asm __volatile("mv %0, tp" : "=&r"(val));
td1->td_pcb->pcb_tp = val;
/* RISCVTODO: save the FPU state here */
}
/* RISCVTODO: save the FPU state here */
pcb2 = (struct pcb *)(td2->td_kstack +
td2->td_kstack_pages * PAGE_SIZE) - 1;
@ -205,15 +194,15 @@ cpu_set_upcall(struct thread *td, void (*entry)(void *), void *arg,
int
cpu_set_user_tls(struct thread *td, void *tls_base)
{
struct pcb *pcb;
if ((uintptr_t)tls_base >= VM_MAXUSER_ADDRESS)
return (EINVAL);
pcb = td->td_pcb;
pcb->pcb_tp = (register_t)tls_base + TP_OFFSET;
if (td == curthread)
__asm __volatile("mv tp, %0" :: "r"(pcb->pcb_tp));
/*
* The user TLS is set by modifying the trapframe's tp value, which
* will be restored when returning to userspace.
*/
td->td_frame->tf_tp = (register_t)tls_base + TP_OFFSET;
return (0);
}