diff --git a/man2/modify_ldt.2 b/man2/modify_ldt.2 index f3cc94d39..daf480e02 100644 --- a/man2/modify_ldt.2 +++ b/man2/modify_ldt.2 @@ -29,14 +29,15 @@ modify_ldt \- get or set a per-process LDT entry .nf .B #include .sp -.BI "int modify_ldt(int " "func" ", void *" "ptr" ", unsigned long " "bytecount" ); +.BI "int modify_ldt(int " func ", void *" ptr ", unsigned long " bytecount ); .fi .PP .IR Note : There is no glibc wrapper for this system call; see NOTES. .SH DESCRIPTION .BR modify_ldt () -reads or writes the local descriptor table (LDT) for a process. The LDT +reads or writes the local descriptor table (LDT) for a process. +The LDT is an array of segment descriptors that can be referenced by user code. Linux allows processes to configure a per-process (actually per-mm) LDT. For more information about the LDT, see the Intel Software Developer's @@ -51,7 +52,8 @@ reads the LDT into the memory pointed to by The number of bytes read is the smaller of .I bytecount and the actual size of the LDT, although the kernel may act as though -the LDT is padded with additional trailing zero bytes. On success, +the LDT is padded with additional trailing zero bytes. +On success, .BR modify_ldt () will return the number of bytes read. .PP @@ -60,7 +62,7 @@ When is 1 or 0x11, .BR modify_ldt () modifies the LDT entry indicated by -.I ptr\->entry_number. +.IR ptr\->entry_number . .I ptr points to a .I user_desc @@ -95,8 +97,8 @@ In Linux 2.4 and earlier, this structure was named The .I contents field is the segment type (data, expand-down data, non-conforming code, or -conforming code). The other fields match their descriptions in the -CPU manual, although +conforming code). +The other fields match their descriptions in the CPU manual, although .BR modify_ldt () cannot set the accessed bit. .PP @@ -128,7 +130,8 @@ When .I func is 2, .BR modify_ldt () -will read zeros. This appears to be a leftover from Linux 2.4. +will read zeros. +This appears to be a leftover from Linux 2.4. .SH RETURN VALUE On success, .BR modify_ldt () @@ -156,7 +159,7 @@ is not equal to the size of the structure .IR user_desc , or .I func -is 1 or 0x11 and the new ldt entry has invalid values. +is 1 or 0x11 and the new LDT entry has invalid values. .TP .B ENOSYS .I func @@ -164,18 +167,14 @@ is neither 0, 1, 2, nor 0x11. .SH CONFORMING TO This call is Linux-specific and should not be used in programs intended to be portable. -.SH BUGS -On 64-bit kernels before Linux 3.19, one of the padding bits in -.I user_desc, -if set, would prevent the descriptor from being considered empty. .SH NOTES Glibc does not provide a wrapper for this system call; call it using .BR syscall (2). .PP .BR modify_ldt () should not be used for thread-local storage, as it slows down context -switches and only supports a limited number of threads. Threading libraries -should use +switches and only supports a limited number of threads. +Threading libraries should use .BR set_thread_area (2) or .BR arch_prctl (2) @@ -184,9 +183,13 @@ calls. .PP The normal use for .BR modify_ldt (2) -is to run legacy 16-bit or segmented 32-bit code. Not all kernels allow -16-bit segments to be installed, however. +is to run legacy 16-bit or segmented 32-bit code. +Not all kernels allow 16-bit segments to be installed, however. +.SH BUGS +On 64-bit kernels before Linux 3.19, one of the padding bits in +.IR user_desc , +if set, would prevent the descriptor from being considered empty. .SH SEE ALSO -.BR set_thread_area (2), .BR arch_prctl (2), +.BR set_thread_area (2), .BR vm86 (2)