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sbpf: undo rodata footprint optimization #1058

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merged 1 commit into from
Dec 12, 2023
Merged

sbpf: undo rodata footprint optimization #1058

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30 changes: 3 additions & 27 deletions src/ballet/sbpf/fd_sbpf_loader.c
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Original file line number Diff line number Diff line change
Expand Up @@ -79,20 +79,6 @@ typedef union fd_sbpf_elf fd_sbpf_elf_t;
#define FD_SBPF_MM_PROGRAM_ADDR (0x100000000UL) /* readonly program data */
#define FD_SBPF_MM_STACK_ADDR (0x200000000UL) /* stack (with gaps) */

/* FD_SBPF_RODATA_GUARD is the size of the guard area after the rodata
segment. This is required because relocations can be partially
out-of-bounds. The largest relocation type is 16 bytes of read/write,
so there should be 16 minus 1 bytes of guard area past the end.
Guard area at the beginning is not required, as the rodata segment
always starts at file offset zero.

Example:

[ RODATA segment ....... ] [ Guard area .................... ]
[ Relocation .................... ] */

#define FD_SBPF_RODATA_GUARD (15UL)

/* _fd_int_store_if_negative stores x to *p if *p is negative (branchless) */

static inline int
Expand Down Expand Up @@ -441,7 +427,7 @@ fd_sbpf_load_shdrs( fd_sbpf_elf_info_t * info,
}

info->rodata_sz = (uint)segment_end;
info->rodata_footprint = (uint)( segment_end+FD_SBPF_RODATA_GUARD );
info->rodata_footprint = (uint)elf_sz;

return 0;
}
Expand Down Expand Up @@ -801,6 +787,8 @@ fd_sbpf_r_bpf_64_64( fd_sbpf_loader_t const * loader,
fd_sbpf_elf_info_t const * info,
fd_elf64_rel const * rel ) {

(void)info;

uint r_sym = FD_ELF64_R_SYM( rel->r_info );
ulong r_offset = rel->r_offset;

Expand All @@ -822,9 +810,6 @@ fd_sbpf_r_bpf_64_64( fd_sbpf_loader_t const * loader,
fd_elf64_sym const * sym = &dynsyms[ r_sym ];
ulong S = sym->st_value;

/* Skip if side effects not visible in VM */
if( FD_UNLIKELY( A_off_lo > info->rodata_sz ) ) return 0;

/* Relocate */
ulong A = FD_LOAD( uint, &rodata[ A_off_lo ] );
ulong V = fd_ulong_sat_add( S, A );
Expand Down Expand Up @@ -876,9 +861,6 @@ fd_sbpf_r_bpf_64_relative( fd_sbpf_elf_t const * elf,
REQUIRE( va!=0UL );
va = va<FD_SBPF_MM_PROGRAM_ADDR ? va+FD_SBPF_MM_PROGRAM_ADDR : va;

/* Skip if side effects not visible in VM */
if( FD_UNLIKELY( imm_lo_off > info->rodata_sz ) ) return 0;

/* Write back
Skip bounds check as .text is guaranteed to be writable */
FD_STORE( uint, rodata+imm_lo_off, (uint)( va ) );
Expand All @@ -889,9 +871,6 @@ fd_sbpf_r_bpf_64_relative( fd_sbpf_elf_t const * elf,
/* Bounds checks */
REQUIRE( (r_offset+8UL>r_offset) & (r_offset+8UL<=elf_sz) );

/* Skip if side effects not visible in VM */
if( FD_UNLIKELY( r_offset > info->rodata_sz ) ) return 0;

/* Read implicit addend */
ulong va = FD_LOAD( uint, rodata+r_offset+4UL );

Expand Down Expand Up @@ -980,9 +959,6 @@ fd_sbpf_r_bpf_64_32( fd_sbpf_loader_t const * loader,
REQUIRE( (r_offset+8UL>r_offset) & (r_offset+8UL<=elf_sz) );
ulong A_off = r_offset+4UL;

/* Skip if side effects not visible in VM */
if( FD_UNLIKELY( A_off > info->rodata_sz ) ) return 0;

/* Apply relocation */
FD_STORE( uint, rodata+A_off, V );

Expand Down
6 changes: 3 additions & 3 deletions src/ballet/sbpf/fd_sbpf_loader.h
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Original file line number Diff line number Diff line change
Expand Up @@ -52,7 +52,7 @@ struct fd_sbpf_elf_info {
uint dynstr_sz; /* Dynstr char count */

uint rodata_sz; /* size of rodata segment */
uint rodata_footprint; /* rodata_sz + FD_SBPF_RODATA_GUARD */
uint rodata_footprint; /* size of ELF binary */

/* Known section indices
In [-1,USHORT_MAX) where -1 means "not found" */
Expand All @@ -77,8 +77,8 @@ typedef struct fd_sbpf_elf_info fd_sbpf_elf_info_t;

[rodata,rodata+rodata_sz) is an externally allocated buffer holding
the read-only segment to be loaded into the VM. WARNING: The rodata
area required doing load (rodata_footprint) is slightly larger than
the area mapped into the VM (rodata_sz). See FD_SBPF_RODATA_GUARD.
area required doing load (rodata_footprint) is larger than the area
mapped into the VM (rodata_sz).

[text,text+8*text_cnt) is a sub-region of the read-only segment
containing executable code. */
Expand Down